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Anyone seeking to utilize +this eBook outside of the United States should confirm copyright +status under the laws that apply to them. diff --git a/README.md b/README.md new file mode 100644 index 0000000..6f67fca --- /dev/null +++ b/README.md @@ -0,0 +1,2 @@ +Project Gutenberg (https://www.gutenberg.org) public repository for +eBook #54241 (https://www.gutenberg.org/ebooks/54241) diff --git a/old/54241-0.txt b/old/54241-0.txt deleted file mode 100644 index 95f86d1..0000000 --- a/old/54241-0.txt +++ /dev/null @@ -1,3376 +0,0 @@ -The Project Gutenberg EBook of The Cubomedusæ, by Franklin Story Conant - -This eBook is for the use of anyone anywhere at no cost and with -almost no restrictions whatsoever. You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org/license - - -Title: The Cubomedusæ - -Author: Franklin Story Conant - -Release Date: February 26, 2017 [EBook #54241] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE CUBOMEDUSÆ *** - - - - -Produced by Donald Cummings, Bryan Ness and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - - - - - - - - - - Memoirs from the Biological Laboratory - OF THE - JOHNS HOPKINS UNIVERSITY - IV, 1 - WILLIAM K. BROOKS, EDITOR - - THE CUBOMEDUSÆ - - A DISSERTATION PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY, - IN THE JOHNS HOPKINS UNIVERSITY, 1897 - - BY - FRANKLIN STORY CONANT - - A MEMORIAL VOLUME - - BALTIMORE - THE JOHNS HOPKINS PRESS - 1898 - - PRINTED BY - The Lord Baltimore Press - - THE FRIEDENWALD COMPANY - BALTIMORE, MD., U. S. A. - - - - -[Illustration: With the kind regards of Franklin Story Conant. - -THE HELIOTYPE PRINTING CO. BOSTON] - - - - -FRANKLIN STORY CONANT - -SEPTEMBER 21, 1870--SEPTEMBER 13, 1897 - -A BIOGRAPHICAL SKETCH - - -This Treatise is printed after the author’s death, as a Memorial by his -friends, fellow-students and instructors, with the aid of the Johns -Hopkins University. It consists of his Dissertation, reprinted from the -copy which was accepted by this University at his examination for the -degree of Doctor of Philosophy in June, 1897. - -As he had made many notes on the embryology of the Cubomedusæ, and -had hoped to complete and publish them together with an account of -physiological experiments with these medusæ, he had described the -Dissertation on the title-page as Part I, Systematic and Anatomical, and -he went to Jamaica immediately after his examination to continue his -studies and to procure new material, and he there lost his life. - - * * * * * - -Franklin Story Conant was born in Boston on September 21, 1870, and he -died in Boston on September 13, 1897, a few days after his arrival from -Jamaica, where he had contracted yellow fever through self-sacrificing -devotion to others. - -He was educated in the public schools of New England; at the University -of South Carolina; at Williams College, where he received the degree of -Bachelor of Arts in 1893; and in the Johns Hopkins University, where he -received the degree of Doctor of Philosophy in 1897, and where he was -appointed a Fellow in 1896 and Adam T. Bruce Fellow in 1897. - -Most of his instructors have told us that they quickly discovered -that Conant was a young man of unusual intelligence and energy and -uprightness, and as his education progressed he secured the esteem and -the affectionate interest of all who had him in charge, so that they -continued to watch his career with increasing pride and satisfaction. - -He entered the Johns Hopkins University in the spring of 1894, and at -once joined the party of students in zoology who were working, under -my direction, in the marine laboratory of the University at Beaufort, -North Carolina; and from that time until his death he devoted himself -continually, without interruption, to his chosen subject--spending his -winters in the laboratory in Baltimore, and devoting his summers to -out-of-door studies at Beaufort and at Wood’s Holl, and in Jamaica. - -It is as a student and not as an investigator that we most remember -Conant, for most of his time was given to reading and study on subjects -of general educational value; although he had begun, before his death, to -make original contributions to science and to demonstrate his ability to -think and work on independent lines. - -His study of the Chaetognaths was undertaken only for the purpose of -verifying the account of their anatomy and development in the text books, -but it soon showed the presence at Beaufort of several undescribed -species. Without interrupting his more general studies, he employed his -odd moments for three years in their systematic analysis, and at last -published two papers, “Description of Two New Chaetognaths,” and “Notes -on the Chaetognaths,” which show notable power of close and accurate -observation and of exact description; and, while short, are valuable -contributions to our knowledge of this widely distributed but difficult -group. - -As he appreciated the value to one who has devoted himself to zoology -of thorough acquaintance with physiological problems and the means for -solving them, he wished, after he had completed his general course in -physiology, to attempt original research in this field; and, at the -suggestion of Professor Howell, he, in company with H. L. Clark, his -fellow student, undertook and successfully completed an investigation of -which Professor Howell gives the following account: - - In connection with Mr. H. L. Clark, Mr. Conant undertook to - investigate the character of the nervous control of the heart - beat in decapod crustaceans. They selected the common edible - crab, Callinectes hastatus, and made a series of most careful - experiments and dissections which resulted in proving the - existence of one inhibitory nerve and two accelerator nerves - passing to the heart on each side from the thoracic ganglion. - They not only demonstrated the physiological reaction of - these nerves, but traced out successfully their anatomical - course from the ganglion to the pericardial plexus. It seemed - hardly probable from an a priori standpoint that in an animal - like the crab there should be any necessity for an elaborate - nervous mechanism to regulate the beat of the heart, but their - experiments placed the matter beyond any doubt, and have since - served to call attention to this animal as a promising organism - for the study of some of the fundamental problems in the - physiology of the heart. As compared with previous work upon - the same subject it may be said that their experiments are the - most definite and successful that have yet been made. - -His chief completed work, the Dissertation on The Cubomedusæ, is here -printed; and through it the reader who did not know Conant must decide -whether he was well fitted, by training and by natural endowments, for -advancing knowledge. I myself felt confident that the career on which he -had entered would be full of usefulness and honor. I was delighted when -he was appointed to the Adam T. Bruce Fellowship, for I had discovered -that he was rapidly becoming an inspiring influence among his fellow -students in the laboratory, and I had hoped that we might have him among -us for many years, and that we might enjoy and profit by the riper fruits -of his more mature labors. - -Immediately after his examination for the degree of Doctor of Philosophy -in June, 1897, he set out for Jamaica to continue his studies at the -laboratory which this University had established for the summer at Port -Antonio, and he there worked for nearly three months on the development, -and on the physiology of the sense-organs, of the Cubomedusæ. - -His notes and specimens are so complete that I hope it will be possible -to complete in Baltimore, at an early day, the work which he had expected -to carry on this year. - -After the sudden and alarming death of the director of the expedition, -Dr. J. E. Humphrey, Conant took the burden of responsibility upon -himself, and while he fully appreciated his own great danger, he devoted -himself calmly and methodically to the service of others who, in their -afflictions, needed his help, and he fell in the path of duty, where he -had always walked, leaving behind him a clear and simple account of all -the business of the laboratory and of his scientific work, and of his own -affairs, complete to the day before his death. - -Immediately after the opening of the University in October his friends -and companions and instructors assembled to express the sorrow with which -they had heard the sad news of his death, and to record their love and -esteem for the generous, warm-hearted friend who in all the relations -of life had proved himself so worthy of their affectionate remembrance. -At this meeting those who had worked at his side in our laboratories -recalled his steadfast earnestness in the pursuit of knowledge, and the -encouragement they had found in his bright example; while those who -had been his instructors spoke of him as one who had bettered their -instruction and enriched all that he undertook by sound and valuable -observations and reflections. While all united in mourning the untimely -loss of one who had shown such rich promise of a life full of usefulness -and honor and distinction, it was pointed out with pride that his end -was worthy of one who had devoted it to the fearless pursuit of truth, -and to generous self-sacrifice and noble devotion to others; and it -was resolved, “That we prize the lesson of the noble life and death of -Franklin Story Conant.” - - - - -LIST OF THE PUBLISHED BIOLOGICAL PAPERS OF FRANKLIN STORY CONANT. - - -1. DESCRIPTION OF TWO NEW CHAETOGNATHS. Johns Hopkins University -Circulars, No. 119, June, 1895. - -2. NOTES ON THE CHAETOGNATHS. Johns Hopkins University Circulars, No. -126, June, 1896. - -3. THE INHIBITORY AND ACCELERATOR NERVES TO THE CRAB’S HEART (_an -abstract_), by F. S. Conant and H. L. Clark. Johns Hopkins University -Circulars, No. 126, June, 1896. - -4. ON THE ACCELERATOR AND INHIBITORY NERVES TO THE CRAB’S HEART, by F. S. -Conant and H. L. Clark. The Journal of Experimental Medicine, Vol. I, No. -2, 1896. - -5. NOTES ON THE CUBOMEDUSÆ (_an abstract_). Johns Hopkins University -Circulars, No. 132, November, 1897. - -6. THE CUBOMEDUSÆ. (This was accepted in June, 1897, as his thesis for -the degree of Doctor of Philosophy, and it is here printed.) - - - - -TABLE OF CONTENTS. - - - PAGE - - INTRODUCTION 1 - - PART I: SYSTEMATIC 3 - - Family I: CHARYBDEIDÆ 3 - - _Charybdea Xaymacana_ 4 - - “ II: CHIRODROPIDÆ 4 - - “ III: TRIPEDALIDÆ 5 - - _Tripedalia cystophora_ 5 - - PART II: GENERAL DESCRIPTION OF THE ANATOMY OF THE CUBOMEDUSÆ 7 - - A. CHARYBDEA XAYMACANA 7 - - a. Environment and Habit of Life 7 - - b. External Anatomy 8 - - 2. Form of Bell 8 - - 3. Pedalia 8 - - 4. Sensory Clubs 9 - - 5. The Bell Cavity and its Structures 10 - - (a) Proboscis 11 - - (b) Suspensoria, or Mesogonia 11 - - (c) Interradial funnels, or funnel cavities 11 - - (d) Velarium 12 - - (e) Frenula 12 - - (f) Musculature 12 - - (g) Nerve ring 13 - - c. Internal Anatomy 13 - - 6. Stomach 13 - - 7. Phacelli 14 - - 8. Peripheral Part of the Gastro-Vascular System 14 - - (a) Stomach Pockets (Valves and Mesogonial Pockets) 14 - - (b) Marginal Pockets 17 - - (c) Canals of the Sensory Clubs and Tentacles 17 - - 9. Reproductive Organs 19 - - 10. Floating and Wandering Cells 20 - - B. TRIPEDALIA CYSTOPHORA 22 - - a. Habitat 22 - - b. External Anatomy 23 - - c. Internal Anatomy 24 - - PART III: DESCRIPTION OF SPECIAL PARTS OF THE ANATOMY 27 - - A. VASCULAR LAMELLÆ 27 - - B. NERVOUS SYSTEM 37 - - LITERATURE 57 - - TABLE OF REFERENCE LETTERS 58 - - DESCRIPTION OF FIGURES 60 - - - - -INTRODUCTION. - - -Jelly-fish offer to the lover of natural history an inexhaustible store -of beauty and attractiveness. One who has studied them finds within him a -ready echo to Haeckel’s statement that when first he visited the seacoast -and was introduced to the enchanted world of marine life, none of the -forms that he then saw alive for the first time exercised so powerful an -attraction upon him as the Medusæ. The writer counts it a rare stroke of -fortune that he was led to the study of a portion of the group by the -discovery of two new species of Cubomedusæ in Kingston Harbor, Jamaica, -W. I., while he was with the Johns Hopkins Marine Laboratory in June of -1896. - -The Cubomedusæ are of more than passing interest among jelly-fish, -both because of their comparative rarity and because of the high -degree of development attained by their nervous system. One fact alone -suffices to attract at once the attention of the student of comparative -morphology--that here among the lowly-organized Cœlenterates we find an -animal with eyes composed of a cellular lens contained in a pigmented -retinal cup, in its essentials analogous to the vertebrate structure. -Perhaps this and other facts about the Cubomedusæ would be more generally -known, had they not been to a certain extent hidden away in Claus’s -paper on Charybdea marsupialis (’78), which, while a record of careful -and accurate work, is in many respects written and illustrated so -obscurely that it is very doubtful whether one could arrive at a clear -understanding of its meaning who was not pretty well acquainted with -Charybdea beforehand. - -Before Claus’s paper was received at this laboratory, H. V. Wilson went -over essentially the same ground upon a species of Chiropsalmus taken -at Beaufort, N. C. When the article on Charybdea marsupialis appeared, -however, the results were so similar that Wilson did not complete for -publication the careful notes and drawings he had made. - -Haeckel’s treatment of the Cubomedusæ in his “System” (’79) in the -Challenger Report (’81) is much more lucid than Claus’s; but the extended -scope of his work and the imperfect preservation of his material -prevented a detailed investigation, and for a more complete and readily -intelligible account of the structure of the Cubomedusæ a larger number -of figures is desirable. - -In the foregoing facts lies whatever excuse is necessary for repeating -in the present paper much that has already seen print in one form or -another. - - - - -PART I: SYSTEMATIC. - - -It seems advisable first of all to establish the systematic position -of the two newly found species, Charybdea Xaymacana and Tripedalia -cystophora. Haeckel’s classification, as given in his “System der -Medusen,” is an excellent one and will be followed in this case. One of -the new species, however, will not classify under either of Haeckel’s -two families, so that for it a new family has been formed and named the -Tripedalidæ. In showing the systematic position of the two new forms, an -outline of Haeckel’s classification will be given, so far as it concerns -our species, together with the additions that have been made necessary. - - -CUBOMEDUSÆ (Haeckel, 1877). - -Characteristics: Acraspeda with four perradial sensory clubs which -contain an auditory club with endodermal otolith sac and one or several -eyes. Four interradial tentacles or groups of tentacles. Stomach with -four wide perradial rectangular pockets, which are separated by four long -and narrow interradial septa, or cathammal plates. Gonads in four pairs, -leaf-shaped, attached along one edge to the four interradial septa. -They belong to the subumbrella, and are developed from the endoderm of -the stomach pockets, so that they project freely into the spaces of the -pockets. - - -Family I: CHARYBDEA (Gegenbaur, 1856). - -Cubomedusæ with four simple interradial tentacles; without marginal lobes -in the velarium, but with eight marginal pockets; without pocket arms in -the four stomach pockets. - - -Genus: _Charybdea._ - -Charybdeidæ with four simple interradial tentacles with pedalia; with -velarium suspended, with velar canals and four perradial frenula. Stomach -flat and low, without broad suspensoria. Four horizontal groups of -gastric filaments, simple or double, tuft or brush-shaped, limited to the -interradial corners of the stomach. - - -Species: _Charybdea Xaymacana_ (Fig. 1). - -Bell a four-sided pyramid with the corners more rounded than angular, -yet not so rounded as to make the umbrella bell-shaped. The sides of the -pyramid parallel in the lower two-thirds of the bell, in the upper third -curving inward to form the truncation; near the top a slight horizontal -constriction. Stomach flat and shallow. Proboscis with four oral lobes, -hanging down in bell cavity a distance of between one-third and one-half -the height of bell; very sensitive and contractile, so that it can be -inverted into the stomach. The four phacelli epaulette-shaped, springing -from a single stalk. Distance of the sensory clubs from the bell margin -one-seventh or one-eighth the height of bell. Velarium in breadth about -one-seventh the diameter of the bell at its margin. Four velar canals in -each quadrant; each canal forked at the ends, at times with more than two -branches. Pedalia flat, scalpel-shaped, between one-third and one-half -as long as the height of bell. The four tentacles, when extended, at -least eight times longer than the bell. Sexes separate. Height of bell, -18-23 mm.; breadth, about 15 mm. (individuals with mature reproductive -elements); without pigment. Found at Port Henderson, Kingston Harbor, -Jamaica. - -As may be seen from the above, C. Xaymacana differs only a little from -the C. marsupialis of the Mediterranean. Claus mentions in the latter -a more or less well defined asymmetry of the bell, which he connects -with a supposed occasional attachment by the proboscis to algæ. In C. -Xaymacana I never noticed but that the bell was perfectly symmetrical. C. -Xaymacana is about two-thirds the size given by Claus for his examples -of C. marsupialis, which were not then sexually mature. It has 16 velar -canals instead of 24 (32), as given by Haeckel, or 24 as figured by -Claus. Difference in size and in number of velar canals are essentially -the characteristics upon which Haeckel founded his Challenger species, C. -Murrayana. - - -Family II: CHIRODROPIDÆ (Haeckel, 1877). - -Cubomedusæ with four interradial groups of tentacles; with sixteen -marginal pockets in the marginal lobes of the velarium, and with eight -pocket arms, belonging to the exumbrella, in the four stomach pockets. - -This family is represented in American waters by a species of -Chiropsalmus, identified by H. V. Wilson as C. quadrumanus, found at -Beaufort, North Carolina. - - -Family III: TRIPEDALIDÆ (1897). - -Cubomedusæ with four interradial groups of tentacles, each group having -three tentacles carried by three distinct pedalia; without marginal lobes -in the velarium; with sixteen marginal pockets; without pocket arms in -the stomach pockets. - - -Genus: _Tripedalia_. - -For the present the characteristics of family and genus must necessarily -be for the most part the same. The genus is distinguished by having -twelve tentacles in four interradial groups of three each; velarium -suspended by four perradial frenula; canals in the velarium; stomach -projecting somewhat convexly into the bell cavity, with relatively -well-developed suspensoria; four horizontal groups of gastric filaments, -each group brush-shaped, limited to the interradial corners of the -stomach. - - -Species: _Tripedalia cystophora_ (Fig. 17). - -Shape of bell almost exactly that of a cube with rounded edges; the roof -but little arched. The horizontal constriction commonly seen near the -top of the bell in the Cubomedusæ not present. Proboscis with four oral -lobes; hanging down in the bell cavity generally more than half the depth -of the cavity and at times even to the bell margin. In the gelatine of -the proboscis an irregular number (15-21) of sensory organs resembling -otocysts, from the presence of which comes the specific name. Phacelli -brush-shaped, composed of from seven to thirteen filaments springing from -a single stalk in each quadrant, or rarely from two separate stalks in -one of the quadrants. Distance of the sensory clubs from the bell margin -about one-fifth or one-fourth of the height of bell. Breadth of velarium -about one-sixth the diameter of bell at margin; with six velar canals in -each quadrant; the canals simple, unforked. Pedalia flattened, shaped -like a slender knife blade, about half as long as the height of the -bell. Tentacles at greatest extension observed two and a half times the -length of pedalia. Sexes separate. Height of bell in largest specimens -(reproductive elements mature) eight or nine mm. Breadth same as height -or even greater. Color a light yellowish brown, due in large part to eggs -or embryos in the stomach pockets. The reproductive organs especially -prominent by reason of their similar color. Found in Kingston Harbor, -Jamaica. - -It will be seen from the above that Tripedalia possesses two of the -characteristics of the Charybdeidæ and two of the Chirodropidæ. The -family was named from the prominent feature of the arrangement of the -tentacles, in groups of three with separate pedalia. The small size of -T. cystophora is worthy of note in connection with the fact that of the -twenty species of Cubomedusæ given by Haeckel in his “System” only two -are smaller than 20 mm. in height, and those are the two representatives -of Haeckel’s genus Procharagma, the prototype form of the Cubomedusæ, -without pedalia and without velarium. While Tripedalia has both pedalia -and velarium, it may be perhaps that its small size, taken in connection -with characteristics just about midway between the Charybdeidæ and the -Chirodropidæ, indicate that it is not a recently acquired form of the -Cubomedusæ. - - - - -PART II: GENERAL DESCRIPTION OF THE ANATOMY OF THE CUBOMEDUSÆ. - - -A: CHARYBDEA XAYMACANA. - - -a. _Environment and habit of life._ - -1. The Cubomedusæ are generally believed to be inhabitants of deep water -which come to the surface only occasionally. Both of the Jamaica species, -however, were found at the surface of shallow water near the shore, -and only under these circumstances. Whether these were their natural -conditions, or whether the two forms were driven by some chance from the -deep ocean into the Harbor and there found their surroundings secondarily -congenial, so to speak, can be a matter of conjecture only. C. Xaymacana -was taken regularly a few yards off-shore from a strip of sandy beach -not ten minutes row from the laboratory at Port Henderson. It was seen -only in the morning before the sea-breeze came in to roughen the water -and to turn the region of its placid feeding-ground into a dangerous -lee-shore. Some of the specimens taken contained in the stomach small -fish so disproportionately large in comparison with the stomach that they -lay coiled up, head overlapping tail. The name Charybdea, then, from -the Greek χαρύβδις (a gulf, rapacious), seems to be no misnomer. It is -worth mentioning that the digestive juices left the nervous system of the -fish intact, so that from the stomach of a Charybdea could be obtained -beautiful dissections, or rather macerations, of the brain, cord, and -lateral nerves of a small fish. - -In size C. Xaymacana agrees very well with the average of the genus. -The four single tentacles characteristic of the genus are very -contractile, varying from two or three to six or seven inches in length, -and probably if measurements could be taken while the animal was -swimming freely about, the length would be found to be greater still. -Charybdea is a strong and active swimmer, and presents a very beautiful -appearance in its movements through the water, the quick, vigorous -pulsations contrasting sharply with the sluggish contractions seen in -most Scyphomedusæ. With its tentacles streaming gracefully behind, an -actively swimming Charybdea presents a fanciful resemblance to a comet -or meteor. When an attempt is made to capture one, it will often escape -by going down into deeper water--as indeed do other jelly-fish. Escape -from observation is all the more easy by reason of the entire absence -of pigment excepting for the small amount in the sensory clubs. The -yellowish or brownish color usually stated as common in the Cubomedusæ is -nowhere present in C. Xaymacana. - - -b. _External Anatomy._ - -2. _Form of Bell._ C. Xaymacana shows the typical division of the -external surface into four almost vertical perradial areas (Figs. -1-3, _p_), separated by four stoutly arched interradial ribs or bands -(Figs. 1-3, _i_). These ribs thus play the part of corners to the -Cubomedusan pyramid. They are formed by the thickenings of the jelly of -the exumbrella, and serve to give the necessary strength to the four -interradial corners, each of which bears one of the four tentacles at -its base. Each rib is further divided into two longitudinal strips by a -vertical furrow lying exactly in the interradius (Fig. 2, _ifr_). The -surface of the exumbrella is thus marked by twelve longitudinal furrows, -as seen in the same figure (2). Of these, four are the interradial -furrows just mentioned; the other eight are the adradial (_afr_) -furrows, which set off the four perradial surfaces of the pyramid from -the four interradial ribs or bands of the corners, each of which is -again subdivided, as mentioned above, by the shallower interradial -furrows. Each interradial furrow ends above the base of the corresponding -pedalium, at about the level of the sensory club; each adradial furrow -diverges toward the perradius in the lower third of its course, and thus -with its companion furrow narrows down the perradial surface of the -pyramid in the lower part of the bell to an area of not much greater -width than the niches in which the sensory clubs lie. The projecting -interradial corners are of course correspondingly enlarged in the lower -part of the bell, and in this way the contours of the surface are changed -from those figured in the view of the bell from above (Fig. 2) to those -of Fig. 3, which represents a view of the bell margin from below. - -3. _Pedalia._ From the base of the interradial corner bands spring the -four pedalia (Fig. 1, _pe_), gelatinous appendages of the margin having -much the same shape as the blade of a scalpel. These in turn bear on -their distal ends, as direct continuations, the long, contractile, simple -tentacles. The relatively stiff pedalia have the same relation to the -flexible tentacles that a driver’s whip-stock has to the long lash. -In the living animal the pedalia are found attached to the margin at -an angle of about 45° with the longitudinal axis of the bell. In the -preserved specimens they are bent in toward the axis by the contraction -of the strong muscles at their base, in which position they are figured -by Claus for C. marsupialis (’78, Taf. I., Figs. 1 and 2). - -The pedalia are in reality processes belonging to the _subumbrella_, as -will be shown in the section treating of the vascular lamella. They are -composed chiefly of gelatine covered with thin surface epithelium and -carrying within the gelatine the basal portion of the tentacle canals. -They have received various names at the hands of the writers. Gegenbaur -called them “Randblätter.” Claus gave them the name of “Schirmlappen,” -and incorrectly homologized them with the marginal lobes of other -Acraspeda. Claus’s error was corrected by Haeckel, who termed them -“Pedalia” or “Gallertsockel,” and homologized them with the pedalia of -the Peromedusæ. Besides furnishing a base of support for the tentacles -they may perhaps also serve as steering apparatus, a function for which -their thin blade-like form would be admirably adapted. - -Internal to the base of each pedalium, between it and the velarium, is -found a funnel-shaped depression of the ectodermal surface. This is -shown in Fig. 5 (_ft_) in longitudinal section, and in cross-section in -Fig. 16. In the latter figure the epithelium of the outer wall of the -funnel (_mt_) is shown much thickened, the result of a stout development -of muscle fibres. These are the muscles that in the preserved specimens -cause the inward contraction of the pedalia referred to above. - -4. _Sensory Clubs_ (marginal bodies, rhopalia). In spite of their -position above the bell margin, the four sensory clubs, representing as -they do transformations of the four perradial tentacles, are properly -classed with the pedalia and interradial tentacles as appendages of -the margin. They lie protected in somewhat heart-shaped excavations or -niches in the perradial areas of the exumbrella. Each sensory niche is -partially roofed over by a covering scale, a hood-like projection from -the exumbrella. Below the covering scale the water has free access to the -niche and to the sensory club within it. The sensory club consists of a -hollow stock directly homologous with tentacle and canal, and a terminal, -knob-like swelling, the sensory portion proper. The latter contains -on its inner surface--the surface turned towards the bell cavity--two -complicated unpaired eyes with lens, retina, and pigment, lying one above -the other in the median line; and at the sides of these, two pairs of -small, simple, pigmented, bilaterally symmetrical eye spots. At the end -of the club, that is, on its lowermost point, lies a sac that contains a -concretion and is usually considered auditory. The canal of the stalk is -directly continuous with the gastro-vascular system. In the swollen knob -of the sensory club it forms an ampulla-like terminal expansion. - -As was pointed out by Claus, the bottom of the sensory niche--by bottom -is meant the vertical wall that separates the space of the niche from -the bell cavity--is formed from the subumbrella only. This arrangement -of parts, apparently impossible for a structure so far removed from -the bell margin as the sensory niche, will be explained more fully -under the special topic of the vascular lamellæ, or cathammal plates. -It is sufficient at this point to refer to Fig. 44, which shows the -shield-shaped area mapped out by a vascular lamella that connects the -endoderm of the stomach pocket with the ectoderm of the bottom of the -niche. By this the exumbrella is completely cut off from any part in the -formation of the bottom of the niche. Cross and vertical sections through -the niche (Figs. 39 and 37) help to a better understanding of these -relations. Since the base of the stalk of the sensory niche lies within -the ring of vascular lamella, the whole organ as well as the bottom of -the niche belongs to the subumbrella, and so in spite of its position -some distance upwards from the bell margin the sensory club is very -properly called a “marginal body” (Randkörper). - -The epithelium of the sensory niche consists entirely of the -flattened ectodermal surface layer common to the whole exumbrella. No -differentiation suggestive of nervous function in addition to that of the -sensory clubs can be discovered, although it would be quite natural to -expect to find something of the sort, as intimated by Claus (’78, p. 27). - -It is worth while to mention again the fact that the eyes are directed -inwardly toward the cavity of the bell. The larger and lower of the two -median eyes looks into the bell cavity horizontally; the smaller upper -eye is turned upward toward the region of the proboscis. This is in the -normal pendant position of the sensory club. The stalk, however, is -very flexible, and a range of other positions of the sense organs is -possible, although nothing was observed to suggest that such positions -were within the control of the animal. The eyes evidently have as their -chief function to receive impressions of what is going on _inside_ the -bell, not outside. Perhaps the strongly biconvex, almost spherical lenses -of the median eyes also point to a focus on near and small objects. - -5. _The Bell Cavity and its Structures._ In general, the bell cavity -repeats the external form of the bell, being almost cubical. In -cross-section it appears very nearly square with the angles in the -interradii as seen in the series of drawings that figure sections of the -whole jelly-fish at different levels (Figs. 6-16). Above, the bell cavity -is roofed over by the stomach; below, it is open freely to the water, -the opening being narrowed somewhat by the diaphragm-like velarium (Fig. -3, _v_); the four flat perradial sides are bounded by the walls of the -four broad stomach pockets, to be described when we come to the internal -anatomy. - -(a) _The Proboscis._ From the stomach there hangs down into the -bell cavity the proboscis or manubrium, which consists of a short -funnel-shaped stalk bearing on its distal end the four mouth lobes or -lips. The latter are somewhat broadly V-shaped processes lying in the -perradii with the convexity directed outwards, and with the concavity -on the inside forming the beginnings of four perradial furrows that are -continued upwards to the stomach. The four furrows are shown in the stalk -of the proboscis in Fig. 11, which represents a section taken a little -above the level of the mouth lobes. The same cross-shaped section of -the stalk shows the four perradial prominences or ridges overlying the -furrows, which are the direct continuations of the four projecting mouth -lobes. - -(b) _The Suspensoria or Mesogonia._ The stomach (leaving out of -consideration the proboscis) hangs down into the bell cavity as a -slightly sagging saucer-shaped roof (Figs. 4 and 5). In the four perradii -it is attached to the lateral walls of the subumbrella by four slenderly -developed mesentery-like structures, the suspensoria or mesogonia. These -are simple ridges of gelatine, covered of course with the epithelium -of the bell cavity, which serve to keep the stomach in position much -in the way that a shelf is supported by brackets (Fig. 4, _su_). The -suspensorium accordingly has two parts, curved so as to lie at right -angles with each other: a vertical portion lying along the wall of the -subumbrella, and a horizontal which passes over from the vertical on -to the basal wall of the stomach. In Fig. 10 the suspensorium in each -quadrant is shown cut across just below the angle between the two parts, -so that the two appear in the section as projections on the wall of the -stomach and on the wall of the subumbrella. - -(c) _The Interradial Funnels or Funnel Cavities._ It will be seen at -once that the four suspensoria serve as partitions to divide the upper -portion of the bell cavity, the part that lies between the stomach -and the lateral walls of the subumbrella, into four compartments. -These compartments extend upwards in the four interradii like inverted -funnels, whence their name. In the series of cross-sections they can be -traced upwards with constantly diminishing area from the level of the -suspensoria, Fig. 10 (_if_), to Fig. 6, which is taken very near the top -of the bell. Homologous structures exist in all the Scyphomedusæ, and in -some of the Lucernaridæ they are continued up even into the stalk of the -attached jelly-fish. - -(d) _The Velarium._ Charybdea, like most of the Cubomedusæ, possesses a -velum-like structure around the opening of the bell cavity (Fig. 3, _v_). -The velarium is a thin muscular diaphragm, resembling the true velum in -position and essential structures, but differing from the velum in its -origin, and in the possession of diverticula from the gastro-vascular -system, the velar canals. Of these there are in C. Xaymacana very -regularly sixteen, four in each quadrant. Their outline is seen in Fig. -3 to be forked with small irregular accessory processes. As for its -origin, the velarium of the Cubomedusæ is commonly accounted to have -arisen by fusion of marginal lobes, as in the case of the velarium of the -Discomedusæ. Pending decisive ontological evidence, the slight notches -in the four perradii seen in Fig. 3 may perhaps be taken as slight -indications of a primitive unfused condition, but the question will be -brought up again when the vascular lamellæ are discussed. - -(e) _The Frenula._ Just as the stomach is attached to the walls of -the subumbrella in the four perradii by the suspensoria, so in the -lower part of the bell cavity the velarium is attached to the wall -of the subumbrella in the perradii by four structures similar to the -suspensoria, the frenula velarii. The frenula, like the suspensoria, -resemble the brackets of a shelf, with the difference that in the case of -the frenula the bracket is above the shelf, their purpose being evidently -to keep the velarium stiff against the outflow of water produced by -the pulsations of the bell. According to the greater need of strength -in this case, we find the frenula stouter, more buttress-like than the -suspensoria. The gelatinous ridge that gives them the necessary firmness -is thickened so as to be triangular in section, as shown in Fig. 16 -(_frn_). - -(f) _Musculature._ As is general in medusæ, the muscular system, so -far as known, is restricted to the subumbrella. It has a very simple -arrangement, consisting of a continuous sheet of circular (_i. e._ -horizontal) striated fibres, which is interrupted only in the four -perradii by the radially directed muscle fibres of the suspensoria and -the frenula. In each quadrant, between the muscle of the suspensorium -above and that of the frenulum below, in an area just internal to the -sensory niche, there lies a space free from muscle. This interruption -of the muscle layer is shown in Fig. 39. Under the head of musculature -belonging to the subumbrella must be included also the radial, or -longitudinal muscles at the bases of the pedalia, which were mentioned -before (Fig. 16, _mt_). The mouth lobes and proboscis also are highly -contractile and muscular. - -(g) _Nerve Ring._ It is in the possession of a clearly defined nerve ring -that the Cubomedusæ differ from all other Scyphomedusæ whose nervous -system has been carefully studied. The nerve ring shows very plainly -on the surface of the subumbrella as a well-defined clear streak. Its -course is zig-zag or festoon-like. In the interradii, at the basis of the -tentacles, it lies not far from the bell margin. In the perradii it rises -to the level of the sensory clubs. This very striking arrangement is -understood at once when it is remembered that the sensory clubs represent -the four perradial primary tentacles, and were originally situated on -the margin. When all the rest of the margin grew down and away from the -four sensory clubs, fusing below them to form the present intact edge of -the bell, the four portions of the nerve ring that lay in the perradii -were left at the level of the sensory clubs, and the originally straight -nerve ring was thus bent into a bow in each quadrant. The finer structure -of the nerve will be treated of in the special part to be devoted to the -nervous system. - - -c. _Internal Anatomy._ - -6. _Stomach._ The shape of the stomach is approximately that of a -biconvex lens, as seen in Fig. 4, which represents a Charybdea cut in -halves longitudinally in the perradius. The lumen of the proboscis (the -buccal stomach according to Haeckel’s terminology) communicates directly -by a funnel-shaped enlargement with the stomach proper, or central -stomach of Haeckel. The term basal stomach is carried over by Haeckel -from the Stauromedusæ, where it has considerable significance, to the -Cubomedusæ, and applied to the upper part of the central stomach. In the -stalkless Cubomedusæ, however, it has no significance so far as actual -structure goes, and our knowledge of the development of the Cubomedusæ is -as yet too simple for us to say that the upper part of the main stomach -represents what remains of the basal stomach of an earlier pedunculated -stage. - -The epithelium of the roof of the stomach is not specially differentiated -and apparently has little or no part in digestion. The epithelium of the -floor, on the other hand, is composed chiefly of very high and thickly -crowded columnar cells which are usually described as coarsely granular, -but under high powers appear to be filled with vacuoles surrounded by -a network of cell substance. Thickly interspersed among these columnar -cells are goblet cells filled with mucus. The floor is thrown into -numerous wrinkles by ridges in the supporting gelatine resulting in -increase of digestive surface. The four perradial grooves of the -proboscis are continued in the perradii along the floor of the stomach -as four fairly deep furrows, which lead directly to the gastric ostia -and stomach pockets--structures to be described presently. These furrows -are lined with crowded columnar cells, smaller and denser than the other -cells of the digestive epithelium, containing no granules and but little -beside the relatively large, compact, deeply staining nuclei. The furrows -probably represent special ciliated courses. - -7. _Phacelli._ Lying in the four interradial corners of the stomach are -the four phacelli or tufts of gastral filaments to the number of thirty -or thirty-five in each tuft. The filaments are attached to a single -stalk, like the fringe of an epaulette or the hairs of a coarse brush. -The stalk bearing the filaments is an outgrowth of the lower wall of the -stomach just at the point where it fuses with the upper. The phacelli are -therefore structures of the subumbrella, proof of which will be found -under the special topic of the vascular lamellæ. The stalk, an indication -of which appears in _sph_. Fig. 6 (the section being a little below the -axis of the stalk, which lies horizontally), consists of a firm core of -gelatine covered with the high columnar epithelium of the floor of the -stomach. The filaments themselves are slender processes repeating the -structure of the stalk and having a central axis of gelatine for support -covered with glandular epithelium, which in the case of the filaments -bears numerous nettle cells. These processes are extremely contractile, -and in the living animal show a continuous, slow, squirming movement -like a mass of worms. The section just referred to (Fig. 6) shows -diagrammatically three of these filaments (_fph_) cut across in each -quadrant. - -8. _Peripheral Part of the Gastro-vascular System._ The proboscis and -stomach proper comprise the central part of the gastro-vascular system. -In direct communication with the central is a peripheral part composed of -pouches or pockets lying in the vertical sides of the cube-shaped bell, -just as the central stomach lies in its roof. The peripheral part may be -subdivided for convenience of description into the stomach pockets, the -marginal pockets, and the canals of the tentacles and sensory clubs. - -(a) _Stomach Pockets._ These are four broad, thin pouches lying between -the exumbrella and the subumbrella in the four perradii (_e. g._ Fig. -9, _sp_) and separated from one another in the interradii merely by four -thin vertical strips of vascular lamella (_ivl_) or fusion between the -two endodermal surfaces of a primitively single undivided peripheral -cavity. The structure is exactly that which we should have if in a -Hydromedusa, for example Liriope (Trachomedusæ), the four radial canals -broadened out and the intervening cathammal plates correspondingly -narrowed, until the relations in size were just reversed, and instead -of four narrow radial canals separated from one another by four broad -cathammal plates, we had four broad radial canals or pouches separated by -four narrow cathammal plates. - -The stomach pockets communicate at their top with the central stomach by -means of four moderately large openings, the gastric ostia. These are -seen in a side view of the whole animal as triangular spaces (Fig. 1, _g. -o._) near the top of the broad perradial sides. In Figures 7 and 8 they -are seen in cross-sections, in Fig. 4 in vertical section. - -The communication between the stomach and each stomach pocket is guarded -by a valve that can cut the one entirely off from the other. The valve is -simply the flexible lower margin of the gastric ostium, a thin vertical -fold of the floor of the stomach, semilunar in shape, just at the point -where it is passing over into the stomach pocket. A longitudinal section, -such as is shown in Fig. 4, gives the best idea of the form and position -of the valve that can be obtained from any simple section. Internal to -the valve is seen a depression of the stomach wall, almost worthy to be -called a pocket. The valve itself lies as a wall across the end of this -depression, obstructing a free course to the stomach pocket. It will be -seen at once that any pressure of fluids in the stomach against this -vertical wall, or valve, would serve only to press it against the inner -surface of the exumbrella, and thus effectually close the entrance into -the stomach pocket. Such a closure would both keep the juices of the -stomach from entering the pockets and the embryos in the pockets from -entering the stomach before the proper time. - -The depression of the floor of the stomach just internal to the valve may -possibly be a structure of some morphological significance. In one series -of sections it was found that in two of the quadrants the depression was -deeper than that represented in Fig. 4, and extended perceptibly into -the outer or vertical portion of the suspensorium. Fig. 32 is a diagram -giving a vertical reconstruction in the perradius of the cross-sections -in which this deepened depression was noticed. Fig. 31 is a drawing -(the outline by camera lucida) of one of the cross-sections, through -the lowermost point of the depression. The figure gives the wall of -the stomach lined with high columnar epithelium (_ens_), and the wall -of the stomach pockets, with the suspensorium (_su_) connecting them. -The section is taken just above the broad angle that lies between the -two parts of the suspensorium, that is, in a plane parallel to the arrow -_a-b_ in Fig. 32, but a little lower down. At the points to which the -reference letter _x_ (Fig. 31) refers are seen the first indications of -the division into two parts, _i. e._ of the apex of the angle. The next -section or two lower down show the relation seen in Fig. 10 (_su_). There -can be no doubt in this case that the depression or pocket lies in the -outer vertical limb of the suspensorium. It is the position that gives -it at least the appearance of some morphological significance. In two -genera of Lucernaridæ named and described by Clark (’78), Halicyathus -and Craterolophus, the mesogonia or suspensoria in all four perradii -contain broad pockets. These mesogonial pockets in the Lucernaridæ have -given rise to considerable misunderstanding owing to the fact that in -some forms the reproductive organs bulge out from the stomach pockets in -which they structurally lie, and come to take up a secondary position -in the walls of the mesogonial pockets. The sections of Charybdea above -referred to indicate that among the Cubomedusæ we may have the same -structure reduced to its lowest terms, and may be a feather’s weight in -favor of the view that the Cubomedusæ are descendants of an attached -Lucernaria-like form. - -Two more diagrams, Figs. 33 and 34, are added in order to give a -more complete understanding of a gastric ostium and its neighboring -structures, the mesogonial pocket and the valve. Fig. 33 is a view of -the gastric ostium and valve from the stomach side, and represents the -appearance that would be given by a thick section through the arrow -_x-y_ in Fig. 32, in a plane at right angles to the paper. The heavy -lines outlining the gastric ostium (_enr_ and _enfl_) represent the -place where the plane of the section has cut across the epithelium of -the roof of the stomach above the ostium and the epithelium of the floor -of the pocket-like depression internal to the valve. The continuation of -the two heavy lines in either side of the ostium represents the region -where the roof and floor of the stomach meet; _i. e._, the edge of the -lens-shaped stomach. The semilunar outline of the valve (_vg_) is shown -by a light line just above the epithelium of the depression. As is seen -by the reference arrow in Fig. 32, the valve lies a little external -to the immediate plane of the section, and hence it is that its inner -surface is seen in Fig. 33 and not a section of it. The vertical part of -the suspensorium (_su_) is seen in section below the epithelium of the -depression. The reference numbers 1, 2, 3 and 4 denote the same points -in Figs. 32 and 33. Fig. 32 referred to Fig. 33 would lie in a plane at -right angles to the paper through the reference arrow _x-v_ of the latter -figure. - -Fig. 34 represents a horizontal section through the gastric ostium at -the level of the arrow _a-b_ in Fig. 32, or arrow _c-d_ in Fig. 33. The -reference numbers 5, 6 and 7, 8 denote similar points in the two figures -33 and 34. Fig. 32 as referred to Fig. 34 is through the arrow _e-f_; -Fig. 33 is through the arrow _c-d_. In the series of cross-sections, Fig. -9 is taken at a level a little below that of Fig. 34, and passes through -the basal part of the valve (_vg_). - -(b) _Marginal Pockets._ The part of the peripheral portion of the -gastro-vascular system in each quadrant which is called the stomach -pocket extends downwards as far as the sensory niche. Here by the coming -together of the walls of the exumbrella and subumbrella the space between -them is obliterated (Fig. 15) in the immediate perradius. From the -sensory niche downward to the margin each stomach pocket is thus divided -into two smaller pouches, the marginal pockets (_mp_). In each side of -the Cubomedusan cube there are, then, in Charybdea two marginal pockets; -or in all eight, a characteristic of the family Charybdeidæ. The marginal -pockets as the name implies extend downwards to the bell margin, and are -continued into the velarium as the velar canals. Of these (Fig. 3) there -are two from each marginal pocket, or sixteen in all. The constancy in -their number is one of the characteristics that distinguish C. Xaymacana -from the very closely related C. marsupialis of the Mediterranean. -(Compare Fig. 3 with the similar one by Claus for C. marsupialis, ’78, -Taf. I., Fig. 6.) The forked shape, while to be sure the common form in -C. marsupialis, is an almost invariable characteristic in C. Xaymacana. -It may be mentioned again that the presence of these canals is one of the -chief features that distinguish the velarium of the Scyphomedusæ from the -velum of the Hydromedusæ. - -(c) _Canals of the Sensory Clubs and Tentacles._ The four interradial -definitive tentacles and the four perradial transformed tentacles, the -sensory clubs, are hollow, and their canals communicate directly with -the peripheral part of the gastro-vascular system. The canal of the -sensory club in each quadrant leads directly out from the stomach by a -somewhat funnel-shaped opening formed by the approximation of the two -walls of the stomach pocket. The relation of the canal of the sensory -club to the stomach pocket is seen at a glance in Fig. 37. It is given -by means of cross-sections in Figs. 12-14. Figure 12 shows the inner -walls of the stomach pocket approaching the outer at two points, leaving -between them a concavity freely open to the rest of the stomach pocket -above and at the sides. Fig. 13, a little lower down, shows the two -walls fused together at two points, making the interspaces a definite -canal communicating with the stomach pocket above only. This canal lies -directly over the sensory niche, and in the next figure (No. 14) the -canal is seen to have passed through the roof of the sensory niche and to -have entered the base of the stalk of the sensory club. In the enlarged -end of the club, the part which bears the sensory structure, the canal -widens into a terminal ampulla-like sac. - -The endoderm lining the canal of the sensory club is specially -differentiated. In the stalk it is more columnar than the epithelium -of the stomach pockets, and is made up of cells containing a brightly -staining nucleus with very little trace of cytoplasm. The cell bodies -appear as if filled with a clear, non-staining fluid. Perhaps these cells -give the stalk elasticity to act in connection with the thin layer of -longitudinal muscle-fibres that are found just external to the supporting -lamella. The epithelium of the terminal enlargement of the canal is -composed of very high narrow cells, many of which show two nuclei of -equal size and staining quality lying side by side. - -In continuation of the specialized epithelium of the perradial furrows -in the floor of the stomach the inner wall of the stomach pocket shows a -strip of similar densely crowded columnar cells leading from the gastric -ostium downwards to the canal of the sensory club. As in the other case, -the strip probably represents a specially ciliated tract, and perhaps -in it we see the reason why the canal of the sensory club is almost -always found to contain either spermatozoa which are shed by the male -reproductive organs directly into the stomach pocket, or else floating -cells of the kind to be described in the next section. - -The canals of the interradial tentacles arise from the peripheral -gastro-vascular system much lower down than those of the sensory clubs, -since these tentacles have preserved their primary positions with -reference to the bell margin. Figure 16 represents a section taken at -the level of the base of the pedalia which gives the connection of the -tentacle canals with the gastro-vascular system. At the level below -the sensory niche the four broad stomach pockets have been divided, as -we have seen, into the right marginal pockets (_mp_). The figure shows -that in the interradial corners the longitudinal septa (_ivl_, in the -preceding figures), or lines of fusion between the two walls of the -peripheral gastro-vascular space, which divide the primitively simple -space into the four stomach pockets, have come to an end, leaving a -connecting canal (_cc_) in each corner as all that remains of the -primitive uninterrupted communication between all parts of the peripheral -system. It is from these four connecting canals that the tentacle canals -take their origin. From this point of origin each tentacle canal passes -downwards, surrounded by the gelatine of the pedalium, into the tentacle -proper. - -The connecting canals are of morphological importance in that they are -supposed, with much reason, to represent in the Cubomedusæ the circular -canal of the Hydromedusæ. - -9. _Reproductive Organs._ The sexes are separate in Charybdea. In both -sexes the reproductive organs consist of four pairs of long leaf-like -bodies, each leaf attached along one edge to the wall of the subumbrella -in an interradius (see Fig. 1, _r_), and hanging free in the stomach -pockets. From this position in the stomach pockets it is evident that -the reproductive organs are endodermal. The lines of attachment of each -pair is just internal to the longitudinal vascular lamella that fuses the -outer and inner walls of the stomach pockets together in the interradius -(_ivl_), and the reproductive organs are therefore structures belonging -to the subumbrella. It is interesting to note how careful examination -of the medusan organization takes away from the importance of the outer -cup, the exumbrella, and adds to that of the inner, the subumbrella. We -have seen that the phacelli and the sensory clubs, from whose position -it would be supposed that they belonged to the exumbrella, are organs of -the subumbrella, and that there is no muscle-tissue in the exumbrella; -we find now that the reproductive organs belong to the subumbrella, and -it will be shown later that the tentacles, like the sensory clubs, are -structures of the subumbrella also. To the exumbrella are left only the -functions of support and covering. - -The mature reproductive organs extend very nearly throughout the entire -vertical length of the bell, and are therefore found in the series of -cross-sections in all but the uppermost and lowermost (Figs. 7-15 _r_). -The organs consist of germ cells within, covered by an epithelium of -columnar cells that shows here and there nettle cells. The ova are -found with different amounts of yolk, according to age, surrounding -a large nucleus almost devoid of chromatin and an intensely staining -nucleolus. In young ova there appears very plainly in every case at -least one small deeply staining body inside the nucleus, which very much -resembles the nucleolus. These are probably so-called yolk nuclei, and -while I have not made a special study of the ovogenesis, I infer that -the constant presence of at least one, points to an origin of the ovum -from a syncytium (of at any rate two cells), similar to that which has -been recently shown by Doflein (’96) to occur in the formation of eggs -in Tubularia. In the nearly mature ovary each ovum is surrounded by a -layer of gelatine, which comes from the gelatinous sheet that enters -the leaf-like ovary for its support along its line of attachment just -internally to the interradial septum. It seems as if the ova, arising -in the epithelium on the surface, pushed their way into the gelatine -inside and there completed their development entirely surrounded by a -slight investment of gelatine, which grows thinner around each ovum as -it increases in size. In males the testes always show a similar division -into compartments by gelatinous meshes, the compartments thus mapped out -being filled with the small brightly staining spermatocytes. Ova and -spermatozoa when mature are set free in the stomach pockets. - -10. _Floating and Wandering Cells._ In the stomach pockets, the canals -of the sensory clubs, and even in the stomach itself, are found in -varying numbers freely floating cells having the appearance of young -ova. They vary in size, the smallest being of the size and having the -general aspect of the small ovocytes found in the ovary. The largest -(Fig. 70) have exactly the same structure as the young ovarian eggs -before they have begun to accumulate yolk. The granular deeply staining -cytoplasm, the clear non-staining nucleus with its bright nucleolus and -the nucleolus-like yolk nucleus, all show beyond doubt that these freely -floating cells originate in the ovary. - -In some of my preparations these cells are found not only floating free, -but wandering through the tissues. Fig. 70 shows two such wandering cells -fixed just as they were making their way either through the digestive -epithelium into the gelatine of the floor of the stomach, or from the -gelatine into the epithelium. The former seems the more probable, though -why they should want to get into the gelatine is not very easy to -conceive. - -Perhaps there is some connection between this and the appearance that the -young ovarian eggs have of pushing their way from the epithelium into -the gelatine of the ovary. And of course it is not impossible that the -whole phenomenon is abnormal, due to rupture of the ovaries which sets -free young ova to exhibit their amœboid tendencies under new conditions. -Against such an explanation, on the other hand, might be urged the fact -that what seem to be the small floating cells are found occasionally -in males as well as females, and that in the females a series can be -traced with a good degree of certainty between the small floating cells -like those found in the walls, and the larger ones which have all the -characteristics of young ova. - -However that may be, this amœboid action of cells having the structure of -ova brings to mind the remarkable form of asexual reproduction described -by Metschnikoff for Cunina proboscidea, under the name of “Sporogonie.” -Unfortunately Metschnikoff’s original paper was not accessible to me, so -that I was unable to obtain more particulars on the subject than those -given in Korschelt and Heider’s text-book (p. 33). The reproductive -organs of both males and females of Cunina proboscidea are said to -produce, besides the usual distinctively sexual elements, neutral amœboid -germ cells, which wander into the endoderm of the stomach and circular -canal, and also penetrate into the gelatine of the subumbrella. These -amœboid cells divide parthenogenetically. One of the two cells of the -first cleavage continues to divide and eventually forms an embryo of -Cunina; the other remains amœboid and serves for movement, attachment and -nourishment of the embryo. - -Charybdea, however, has shown no sign of any such reproductive process -on the part of its floating and wandering cells. The only indication -that I get as to their use points to a possible nutritive function. -The enlarged terminal portion of the canal of the sensory club almost -invariably contains a number of the small-sized floating cells. These -have a vacuolated, half disintegrated appearance, with the nucleus always -compact and brightly staining. Now, examination of the high columnar -cells that line the enlargement of the canal shows the presence in the -cells of bodies of exactly the same appearance as those in the lumen. -In one case a floating cell was found just at the end of an epithelial -cell, to all appearance half ingested. The identity of the bodies inside -the cells and those in the lumen is shown very clearly in some sections -of material fixed in formalin, which preserves nuclei, cell walls and -general outlines well enough, but does not retain the cytoplasm, and -hence is useless for most purposes of histology. In the endodermal -cells of the terminal enlargement thus preserved are found all the more -distinctly the bright, compact, degenerated nuclei of the ingested cells, -while in the lumen are seen other bright, compact nuclei with the poorly -preserved remains of cell substances around them. In addition to the -evidence from the appearance of the floating cells themselves and their -ingestion by the endodermal cells, a little collateral evidence may -perhaps be brought in from the Tripedalia about to be described. From -the ovaries in this form are detached masses of cells (Fig. 71) which -float free in the stomach pockets among the developing embryos, and to -judge from the vacuolation that appears, are used up in their favor. -These cell masses are described more fully in the part on Tripedalia. - - -B: TRIPEDALIA CYSTOPHORA. - - -a. _Habitat._ - -The species upon which the new family was founded was obtained in great -abundance in one locality in Kingston Harbor in the summer of 1896. The -environment was even more unlike that in which Cubomedusæ have been -found heretofore than in the case of Charybdea Xaymacana. On the west -side of the Harbor there is a part more or less cut off from the main -body of water, and so from the ocean, by a peninsula. This sheltered bay -is dotted with small mangrove islands which toward the head of the bay -become so numerous as virtually to convert it into a mangrove swamp. The -water is shallow and discolored with organic matter, showing that the -tide does not exercise much influence here, and the bottom is for the -most part a black mud, deep enough to make wading very uncomfortable -but not impossible near shore. The islands rise but slightly above the -level of the waters, and the thick vegetation that covers them, for the -most part mangroves, grows out into the water on all sides, forming a -fringe of overhanging boughs. It was here in the shelter of the boughs, -among the roots and half-submerged stems of the mangroves, that the small -Cubomedusa was found to thrive. It could be obtained in great abundance -almost any day, and of all sizes from the largest adults with stomach -pockets filled with eggs or embryos down to small specimens only about -two millimeters in diameter. In but one other place was Tripedalia found, -and that was a similar region of half landlocked water skirted with -mangroves, situated near Port Royal, across the harbor from the locality -just mentioned. It would be hard to find places in which the conditions -of life were more strikingly different from those of the pure deep sea -in which the Cubomedusæ have been generally found before. The slight -brownish yellow pigment made the small medusæ a little difficult to see -in the discolored water, but like the pellucid Charybdea in the clear -water of the harbor, their active movements gave away their presence. -The swimming was very vigorous and was effected by quick, strong -pulsations (as many as 120 per minute were counted), very different from -the slow, rhythmic contractions of the Discomedusan Cassiopea which -was found in the same region over by Port Royal. Whether or not the -animal made intentional efforts to escape capture could not be decided -satisfactorily, but certain it was that they did escape often enough by -swimming quickly below the surface of the semi-opaque water. - -Tripedalia endured captivity much more hardily than the Charybdea, and -would live in aquaria happily enough for a number of days--no attempt was -made to see how long. Specimens with their stomach pockets filled with -ripe spermatozoa, or with young at any stage from egg to planula, were -taken in plenty from the latter part of June to the latter part of July. -In each female the young were all at the same stage. The embryos were -thrown out in the aquaria as free-swimming planulæ, which settled down on -the bottom and sides of the glass in a day or two, and quickly developed -into small hydras with mouth and typically with four tentacles (and four -tænioles, W. K. B.), though three and five were by no means uncommon. -In this condition they lived for three weeks without essential change, -and they were still giving no promise of further development when the -laboratory broke up and the jars had to be emptied. - - -b. _External Anatomy._ - -The structure of the Cubomedusæ seems to be that of a type well -established, and accordingly offers no very wide range of diversity among -the different genera. The Charybdea that has just been described is a -very typical form and will serve well as a standard with which to compare -our species of Tripedalia. The resemblances are so close that a detailed -account of the anatomy of the second form would involve much needless -repetition. It is hardly necessary to do more than merely point out in -what points Tripedalia resembles Charybdea and in what points it differs. - -The form of the bell is less pyramidal than in Charybdea. Some -measurements even gave the breadth greater than the height. The external -surface is divided, as typical for the Cubomedusæ, into the four -perradial sides and the four convex interradial ridges, and the furrows -that separate these areas are with one small exception exactly the same -as those of Charybdea, as may be seen by comparing the series of sections -of Tripedalia (Figs. 21-30) with those of Charybdea (Figs. 6-15). The -exception is almost too slight to mention. The adradial furrow in each -octant which sets off the corner rib from the perradial surface in the -lower part of the bell is not directly continuous, as in Charybdea, with -the corresponding furrow in the upper part of the bell--that is, the -_afr´_ of Figs. 24-27 is not continuous with the _afr_ of Figs. 22 and -23, as is seen by both being shown in Fig. 24. The upper furrow (_afr_) -is continued only a short distance, however, below the starting point of -the lower (_afr´_). - -The pedalia conform entirely to the description given those of Charybdea, -except that there are three attached to the bell margin in each -interradius instead of one, and that the blade of each pedalium is much -narrower. - -The sensory clubs also show exactly the same relation to the bell and -exactly the same structure. - -In the bell cavity the proboscis has a longer and better defined stalk -than that of Charybdea, and has the further and more important difference -of possessing special sensory organs, to the number of fifteen or twenty. -The suspensoria are much more developed than in Charybdea, so that the -interradial funnels lying between are more marked. In a corresponding way -the frenula are larger and stouter (Figs. 28, 29, _frn_). The musculature -shows no new features and differs only in being comparatively more -strongly developed and having a more pronounced striation. The nerve ring -follows the same looped course from the margin in each interradius up to -the level of the sensory clubs in the perradius. - - -c. _Internal Anatomy._ - -The stomach offers no peculiarities, and the phacelli also agree with -those of Charybdea except in having a smaller number of filaments in each -tuft. The stomach pockets are not guarded by such well-developed valves -as those described for Charybdea, though the valvular nature of the lips -of the gastric ostia is indicated and the valvular functions undoubtedly -performed. The gastric ostia are smaller (cf. Figs. 7 and 22), and this -makes highly developed valves less necessary. No trace of anything -corresponding to mesogonial pockets was noticed. - -In the matter of the marginal pockets, however, we find that the -agreement with Charybdea is no longer continued. The regions that -correspond to the eight marginal pockets of Charybdea are formed, as in -that genus, by the coming together of the exumbrella and subumbrella at -the sensory niche (Figs. 25-28), but each of these regions is subdivided, -as it is not in Charybdea, into two marginal pockets, a larger (_mp_, -Figs. 28-29) and a smaller (_mp´_). In this way sixteen marginal pockets -are formed as in the Chirodropidæ. Furthermore, as happens in the latter -family but does not in the Charybdeidæ, the marginal pockets extend into -the velarium. From each of the larger marginal pockets are given off two -velar canals, while each of the smaller gives rise to but one short one -(Fig. 18). Fig. 30 represents one of the last sections of a Tripedalia -cut transversely, in which nothing but the pedalia and the velarium -appear, and in it are shown the velar canals (_vc_), which come from the -larger marginal pockets. The velarium appears in four segments because it -is drawn upwards in the four perradii by the frenula (see Fig. 20). That -the canals from the smaller pockets do not appear in the section is due -to their shortness and to the fact that they are pulled upwards above the -level of the sections by the frenula, together with that portion of the -velarium. - -The smaller velar canals, a pair in each perradius, seem to have in -the males some function in connection with the storing of matured -spermatozoa. In specimens with ripe testes they are very often found -crowded to distension with spermatozoa, while the other velar canals may -or may not contain them, and generally do not. The epithelium lining -them is, like that of the others, composed of columnar cells higher on -the wall turned toward the bell cavity than on that turned towards the -exterior, but otherwise not specially differentiated. I searched in -vain for any trace of opening by which the spermatozoa might gain the -exterior. Fig. 29 shows another point which may be mentioned in passing, -namely, that the canal of each of the three tentacles opens into the -peripheral gastro-vascular system independently. The central tentacle -of each group is the homologue of the single tentacle of Charybdea, and -is formed in Tripedalia before the two lateral tentacles appear. Its -communication with the peripheral pocket system is higher up than the -openings of the lateral tentacles, so that in the section drawn the -latter are just beginning to be indicated (_ct´_). - -It remains only to speak of the reproductive organs of Tripedalia. The -sexes are separate in this form also, and ovaries and testes have the -same structure as is found in other Cubomedusæ. The development of -floating masses of cells in the females, however, is a feature which, so -far as I know, has not been observed before. These masses, of which a -small one is represented in section by Fig. 71, are apparently developed -along with the eggs, and repeat the structure of the ovary to all intents -the same as if they were various-sized fragments of it broken loose. -They consist mostly of high, columnar epithelial cells surrounding a -few central cells and showing here and there a nettle cell just as the -reproductive organ does. The epithelial cells differ from those of the -ovary in containing one or more large vacuoles, and this vacuolation -increases as the embryos, among which the masses float, develop. The idea -naturally suggests itself, therefore, that they serve for nourishing -and perhaps for protecting the embryos while they are developing in the -stomach pockets of the mother individual. - - - - -PART III: DESCRIPTION OF SPECIAL PARTS OF THE ANATOMY. - - -A: THE VASCULAR LAMELLÆ. - -In Medusæ it is a common thing to find that in certain definite places of -the gastro-vascular system two endodermal surfaces that were primarily -separated by a space have come together and fused into a single lamella -or plate. Such a structure is called indifferently a cathammal plate, -an endodermal lamella, or a vascular lamella. In the adult animal the -vascular lamellæ are by virtue of their very nature formations “with a -past.” They are scaffolding left in the completed structure, giving us -clues as to the way in which that structure was brought about; and in the -Cubomedusæ, whose development is as yet unknown, they therefore afford an -unusually interesting subject for special consideration. - -The vascular lamellæ that are found in Charybdea and Tripedalia may for -convenience be described as forming two systems, the internal and the -marginal. The former comprises the endodermal fusions that separate the -stomach from the stomach pockets (except for the spaces of communication -left free, the gastric ostia) and those that separate the stomach pockets -from one another. The marginal system consists of the lamella that -connects _endoderm_ of the gastro-vascular system with _ectoderm_ of -the surface in a ring all around the bell margin, and with it also the -vascular lamella of the sensory niche, which has already been referred -to in the general description of Charybdea. The lamellæ of the internal -system have been described by previous writers, and especially by Claus -in his paper on Charybdea, but they are still in need of comprehensive -and clear treatment. The lamellæ of the margin and of the sensory niche -have also been described by Claus, but not thoroughly or with entire -accuracy, nor did he recognize the vascular lamellæ of the sensory niche -as originally a part of the lamellæ of the margin. This last was first -determined by H. V. Wilson upon specimens of Chiropsalmus quadrumanus -obtained at Beaufort, North Carolina. Professor Wilson’s unpublished -notes on Chiropsalmus were very kindly placed in my hands, and so far -as the vascular lamellæ are concerned my own work is only a confirmation -and amplification of his, since Charybdea and Tripedalia in this respect -agree with Chiropsalmus. - -The vascular lamellæ of the internal system are the most prominent and -morphologically the most important. They comprise the four vertical -strips of fusion that separate the four stomach pockets in the interradii -(_ivl_ in the figures of the series of cross-sections of Charybdea and -Tripedalia, Nos. 6-15 and 21-29), and four curved horizontal cross-pieces -at the top of these which separate the stomach from the stomach pockets, -and would make the separation complete did they not leave in each -perradius a free space between their ends, which makes possible the -gastric ostia. - -The arrangement of this internal system of vascular lamellæ is simple. -What they amount to is a certain definite number of linear adhesions -between the two walls of an originally undivided gastro-vascular space, -by which that space is divided up into a central stomach and a peripheral -portion, and the peripheral portion thus further divided into the four -stomach pockets. Perhaps the idea may be conveyed by likening the whole -medusa to a couple of bowls fitting closely one within another and -plastered together at the margins. The exumbrella then would correspond -to the outer bowl, the subumbrella to the smaller inner bowl, and the -original undivided gastro-vascular space to the space between the two. -If now the walls of the space be cemented together in four horizontal -curved lines just in the plane where the bottoms are bending round to -become the sides of the bowls, leaving four interspaces between the ends -of the lines, we should have the original space divided into a central -horizontal somewhat lens-shaped region between the bottoms of the two -bowls that would correspond to the central stomach, and a peripheral -vertical portion between the sides of the bowls that would correspond to -the peripheral gastro-vascular system; central and peripheral portions -would communicate by the four interspaces between the lines of fusion, -which would correspond to the four gastric ostia. If, further, the -vertical peripheral portion be subdivided by four more lines of fusion -running vertically at equal distances apart, each connecting above -with the middle point of the corresponding horizontal line of fusion, -we should have the simple peripheral portion divided into four parts, -corresponding to the stomach pockets, by four vertical lines of fusion, -corresponding to the four interradial vascular lamellæ, the _ivl_ of the -figures. - -These mutual relations of stomach, stomach pockets and lamellæ will -perhaps be made clearer if a comparison is drawn between them and the -similar structures of a Hydromedusa. Liriope, one of the Trachomedusæ, is -a good form to take for such a comparison, since by reason of its direct -development from the egg it is free from the complications of hydroid -medusæ. The young medusa has at first a simple, undivided gastro-vascular -cavity which later is divided up into the central stomach and the -typical radial to circular canals of the Hydromedusæ by means of fusions -between the two endodermal surfaces. Diagrams _a_, _b_ and _c_ of Fig. -35 represent very schematically this process of division into stomach -and canals. In _a_ we have a projection upon a plane surface of the -primary, undivided gastro-vascular cavity, as seen from above; _b_ shows -the first four points of fusion in the interradii; _c_ represents those -four points expanded by growth in all directions into broad cathammal -plates in such a way as to leave the stomach in the centre, the radial -canals in the perradii, and the circular canal in the periphery as all -that remains open of the primary simple cavity. These broad plates -of vascular lamella, separating the narrow radial canals, persist in -the adult Liriope to tell the tale of the formation of the definitive -gastro-vascular system. It seems to me that we are justified by analogy -in drawing a similar conclusion for the Cubomedusæ. In _d_ of Fig. 35 is -represented a projection of a Cubomedusa, in which the homology of the -stomach pockets with the radial canals of the Hydromedusa, and of the -narrow strips of fusion with the broad cathammal plates, is shown at a -glance. To make the comparison more perfect we have only to remember that -in the Cubomedusæ there exists below each interradial vascular lamella a -connecting canal (Figs. 16, 29 and 35 _d_, _cc_) uniting the two separate -adjacent pockets. This, as has been pointed out by other writers, is the -representative of the circular canal of the Hydromedusæ. Practically the -only difference between the structure of the gastro-vascular system of -the Cubomedusæ and that of a form such as Liriope, is that in the latter -the fused areas have broadened out at the expense of the radial canals, -while in the Cubomedusæ on the contrary they have become long and narrow. - -One is strongly tempted by the foregoing comparison to speculate a little -as to whether the reproductive organs of the Cubomedusæ, which lie _in_ -the stomach pockets and are generally supposed to be endodermal, may not -bear some closer relation to those of the Trachomedusæ, which lie “in the -course of” the radial canals (Lang’s Text-book) and by common consent -are ectodermal. And while we are being led by facts such as those just -mentioned above to wonder just a little whether after all the position -of the Cubomedusæ among the Acraspeda is so firmly assured--doubting -some, yet in the frame of mind of one who “fears a doubt as wrong”--the -velarium suggests itself as another point in question. Haeckel does not -hesitate to state emphatically that the velarium of the Cubomedusæ and -the velum of the Craspedote medusæ are only analogous, but the reasons -that he gives (sie sind unabhängig von einander entstanden, und ihre -Structur ist zwar ähnlich, aber keineswegs identisch; namentlich das -Verhalten zum Nervenring ist wesentlich verschieden: System, p. 426) -somehow do not produce so much impression upon one as the very velum-like -appearance of the velarium itself. The origin from the fusion of marginal -lobes is not as yet a matter of observation, and the relation to the -nerve ring is not essentially different from that of the velum to the -lower (_i. e._ inner) nerve ring in the Craspedotæ. The four frenula and -the diverticula from the gastro-vascular system seem to be the chief -differences in structure after all, and these Haeckel evidently did not -think worth mentioning. This speculation, as to the possible relation of -the Cubomedusæ to such forms of the veiled medusæ as Liriope, though it -may be very tempting, is scarcely fruitful enough to repay much effort -on the part of either reader or writer. The whole subject must remain -uncertain until the facts of the development of the Cubomedusæ are known. - -If the structure of the vascular lamellæ of the internal system has been -made clear, the appearances of the vertical and horizontal components in -the figures will be understood without much further explanation. The four -vertical strips in the interradii (_ivl_) have been already referred to -in the figures of the cross-sections of both Charybdea and Tripedalia. In -the longitudinal sections of the two jelly-fish through the interradii, -the vertical lamellæ are cut throughout their entire length from stomach -to connecting canals (Figs. 5-20, _ivl_). The horizontal cross-pieces at -the tops of the vertical lamellæ also appear in several of the figures. -Fig. 36 represents the appearance that would be given by a longitudinal -section taken through any portion of the upper part of the bell except -in the interradii, or in the perradii, through the gastric ostia. The -horizontal vascular lamella (_hvl_) is shown connecting the endoderm -of the stomach (_ens_) with that of the stomach pocket (_enp_). In a -longitudinal section directly through an interradius (Fig. 5 or 20) the -horizontal lamella is cut just at the point where it joins the vertical, -so that the two are not differentiated. In a section through the region -of a perradius (Fig. 4 or 19) the horizontal lamella is of course not -cut, since the section passes through the gastric ostium, whose existence -is conditional upon fusion not having taken place between the endodermal -surfaces. - -The first figure in each of the series of cross-sections (Figs. 6 and 21) -also shows the horizontal vascular lamella, cut across slantingly twice -in each quadrant as it passes between the gelatine of the ex- and of the -subumbrella to connect the epithelium of the stomach with that of the -stomach pocket. The fact that more of the lamella does not appear in such -a cross-section only shows that its course is not perfectly horizontal. - -The region in which the same lamella lies is indicated in the surface -view of the top of the bell of Charybdea (Fig. 2) by the bent line _hvl_ -in each quadrant. The figure manifests the appropriateness of Claus’s -name for the horizontal lamella--“bogenförmige Verwachsungs-Streifen.” -Haeckel calls the same structures “Pylorus-Klappen,” and in his account -of Charybdea Murrayana in the Challenger Report, speaking of the three -divisions of the stomach (buccal, central and basal) which he traces -upwards from the stalked forms of Scyphomedusæ, he says: “The central -stomach in this Charybdea, as in most Charybdea, is joined to the basal -stomach, as the pyloric stricture between the two is not developed and -only faintly indicated by the slightly projecting pyloric valves.” -Again, in speaking of the valves of the gastric ostia, he says: “These -four perradial ‘pouch valves’ alternate with the interradial pyloric -valves.” It is difficult to understand, however, how the “bogenförmige -Verwachsungs-Streifen” of Claus, which are undoubtedly the same -structures as those which I have called the horizontal lamellæ, and are -only strips of endodermal fusion, can be “projecting pyloric valves,” or -indeed can properly be spoken of as valves at all. Possibly Haeckel was -not quite able to understand Claus’s description, and in his desire to -find something in the stomach of Charybdea which would serve to set off a -central from a basal part, such as is found in the Lucernaridæ, hit upon -Claus’s “Verwachsungs-Streifen.” I have elsewhere given it as my opinion -that in such of the Cubomedusæ as I have studied there is no structure in -evidence that would properly serve to mark a limit between a basal and a -central portion of the stomach. - -We have next to describe the marginal system. The vascular lamellæ -mentioned above in every case connected endoderm of one cavity with -endoderm of another; those of the margin have the noteworthy difference -that they run from endoderms of some part of the gastro-vascular system -to _ectoderm of the surface_. The outermost cells of the endodermal -lamellæ make direct connection with the ectodermal cells, without the -usual intervention of a layer of gelatine. - -The marginal lamella of Charybdea lies, as the name implies, just on the -bell margin where the edge is curving round into the velarium. All around -the whole circumference of the bell it is found (in Charybdea) at this -same horizontal bend, except in the eight principal radii, where the -tentacles and the sensory clubs have brought about modifications. In any -place except these a vertical section through the margin will show the -marginal lamella connecting the endoderm of the marginal pocket with the -ectoderms of the surface, as represented by _vlm_ in Fig. 38, which is a -vertical section through the sensory niche a little to one side of the -perradial axis. - -In the interradii the marginal lamella undergoes modifications due to the -fact that the bases of the pedalia are situated a little upwards from -the exact margin, and that the lamella follows the outline of the bases. -Fig. 1 shows one of the interradial corners of the bell margin looked at -directly from the surface, so that the curved outline of the junction of -the base of the pedalium with the exumbrella is seen. The trace made by -the lamella where it meets the surface ectoderm follows this outline. The -lamella is also shown in the vertical section through the interradius -(Fig. 5 or 20, _vlm_), where it is seen running from the connecting -canals (_cc_), which joins the two adjacent marginal pockets, upwards and -outwards to meet the surface ectoderm. Its course from canal to surface -is not in a direct line, but curved with the concavity upwards. Hence, in -cross-sections at certain levels through the interradial corner it is met -more than once and gives rise to appearances that seem at first sight too -complicated for it to be just the same structure as the simple marginal -lamella described above. That it is the same, and that the complication -is only due to the insertion of the pedalia above the margin, can be -determined by following through a series of cross-sections, the essential -ones of which, as I hope, are given in Figs. 40-43. The levels of these -are shown on Fig. 5 by the letters _w_, _x_, _y_ and _z_, respectively. -Fig. 40 shows the lamella cut but once, just below its highest part. The -section is above the level of the connecting canal and hence still shows -the vertical interradial lamella _ivl_. Fig. 41, at the next lower level -(_x_), shows the same portion of the lamella intersected a little nearer -the interior, while the junction with the endoderm of the connecting -canal is shown still further inside. Fig. 42 is at level _y_, just -through the bend of the loop, so that in part of its course the lamella -is cut almost horizontally, _i. e._ in its own plane. Fig. 43 finally -shows the lamella as it appears below the level of the connecting canal, -cut twice, each portion joining endoderm of marginal pocket with ectoderm -of surface. It thus bears exactly the same relations that it had when we -first met it in Fig. 38 (_vlm_), except that here in Fig. 43 one finds -that a cross-section cuts it at right angles instead of a vertical as in -Fig. 38, as a result of its being pushed upwards from its former position -on the margin by the insertion of the pedalium above the margin. - -The vascular lamella of the sensory niche has already been alluded to as -part of the marginal system, and brief reference has been made to it in -the section on the sensory clubs. Like the rest of the marginal lamella, -it connects endoderm with ectoderm. The line that its fusion with the -ectoderm traces on the surface frames in a shield-shaped area at the -bottom of the sensory niche, which is seen in the drawing of the outlines -of the niche, Fig. 44 (_vls_). This lamella was observed by Claus, and -was figured by him both in surface view and in cross-section through the -niche. Apparently, however, he omitted vertical sections through the -niche, so that he supposed that the outline traced by the lamella was -not continuous above, _i. e._ over the stalk of the sensory club (’78, -Fig. 41; text, p. 28). That the outline is closed above, though masked -in surface view by the roof of the sensory niche, is seen at once in -vertical sections, such as Figs. 37 and 38, one of which is directly -through the perradius, the other a little to one side. Both show the -vascular lamella of the sensory niche (_vls_) intersected twice, above -and below the sensory club, and completely cutting off the exumbrella -from any share in the bottom (or inner wall) of the sensory niche. Fig. -39, which is a cross-section through the upper part of the niche, and is -essentially like the similar figure of Claus, shows in like manner that -the bottom of the sensory niche belongs to the subumbrella. H. V. Wilson -was the first to point out, in his unpublished notes, that the lamella of -the niche is complete all round. - -In the adult structure of Charybdea and Tripedalia the lamella of -the niche is connected with that of the margin by a vertical strip -of endodermal fusion that does not come to the surface like the rest -of the marginal system, but remains just internal to the gelatine of -the exumbrella, connecting the two adjacent marginal pockets. In the -cross-sections of Charybdea it is seen in Fig. 16 (_vlc_); in those of -Tripedalia it is seen in Figs. 28 and 29. In vertical section it is found -in Figs. 4, 19 and 37. In Fig. 44, which represents the bell margin -and velarium of Tripedalia arranged as if the velarium were vertical -and pendant from the margin (instead of suspended by the frenulum so as -to be at right angles to the vertical plane), the connecting lamella is -shown as a dotted line (_vlc_)--dotted because it does not come to the -surface--joining the lamella of the niche with that of the margin (_vlm_). - -The same figure (No. 44) shows a characteristic difference between the -marginal lamella of Tripedalia and that of Charybdea. While in Charybdea, -as Claus points out, the marginal lamella keeps at one level, just a -little above the bell margin, all the way round (except where disturbed -by the special modifications of the tentacles and the sensory clubs), -and never descends into the velarium, in Tripedalia on the other hand -it describes a sinuous course, following the outlines of the marginal -pockets, as is indicated in the figure by the light parallel line _vlm_. -The course as it would be seen in a surface view is obscured just at -each side of the interradius by the overhanging of the bases of the two -lateral pedalia. This is why the lamella is not indicated at these points -in the diagram. The course is seen to lie almost wholly on the velarium, -that is, in the figure below the line which represents the bell margin -proper, the line at which the angle comes when the velarium is in its -normal position, horizontal to the vertical side of the bell. - -In this sinuous course of the marginal lamella we have another point of -resemblance between Tripedalia and the Chirodropidæ. H. V. Wilson worked -it out in his sections of Chiropsalmus, and the reconstruction which I -have given in the figure under discussion is in all essentials similar -to his for Chiropsalmus. The differences lie only in the fact that -Chiropsalmus has more velar canals, and that the chief marginal pocket -in each quadrant is not forked peripherally, as is that of Tripedalia -(_mp_), but presents its distal margin parallel to the edge of the -velarium. The two smaller marginal pockets in the perradii (_mp´_) are on -identically the same plan in both. - -Tripedalia, having three tentacles joining the umbrella in each -interradius, shows a disturbance of the course of the marginal lamella in -these regions by just so much the more complicated than in Charybdea. The -plan, however, is exactly the same. The lamella is pushed upwards from -the margin by each of the bases of the three pedalia just as is done by -the base of the single pedalium of Charybdea. Fig. 29 shows the lamella -in the same relation to the canal of the central tentacle (_ct_) that -it has in the similar sections of Charybdea (Figs. 16 and 43); and in -addition the first appearances (as the series is traced downwards) of -the arches of the lamella over the two lateral tentacles (_ct´_), which -are inserted a little lower down than the middle one of the group. As -concerns these lateral tentacles, the relations of the vascular lamella -at this level are the same as that in the level of Fig. 40 for Charybdea. - -It has been stated more than once already that the vascular lamella of -the sensory niche is a part of the lamella that runs round the margin, -and so far the only evidence given has been the strip of endodermal -fusion running from the marginal lamella to that of the niche. This -strip, however, as has been described, does not come to the surface and -consequently seems at first sight to be a different structure from the -lamella of the margin. That it is not, however, I found very prettily -shown in a series of sections of one of my youngest Tripedalia. In -this the lamella of the niche as it was traced in successive sections -downwards, was found not to form a closed ring at the bottom of the -niche, but each side was continued directly and separately downwards to -the margin, where it passed into the corresponding part of the marginal -lamella. A reconstruction of the condition, similar to that of Fig. 44, -is given in Fig. 45, and I think explains itself at a glance. Evidently -the vascular lamellæ that connect the lamella of the sensory niche with -that of the margin at first come to the surface, like the rest of the -marginal system, but as the animal grows older come to lie within the -gelatine. In this way the condition found in cross-sections just through -the margin of my very small Tripedalia, and represented in Fig. 46, -becomes that of the adult seen in the corresponding portion of Fig. 29. -It is as complete a demonstration as could be required that the lamella -of the sensory niche is at first only a loop of the marginal lamella, a -conclusion that had been already reached by H. V. Wilson on theoretical -considerations, based upon the facts of the adult structure as he found -them in Chiropsalmus. - -As Wilson pointed out in his notes, these facts have a close bearing upon -the question of the origin of the velarium. Sixteen marginal pockets -are found in both Chiropsalmus and Tripedalia, and all of them extend -into the velarium. It is not unnatural to suppose that these belong to -sixteen marginal lobes, and that these lobes have fused together to form -the velarium. In the Chirodropus figured by Haeckel (Taf. XXVI) in his -“System” gelatinous lobe-like thickenings are shown in the velarium, -corresponding to the sixteen marginal pockets. In Tripedalia no special -gelatinous thickenings are found, but the arrangement of the marginal -pockets is the same as that of the Chirodropidæ, and perhaps I ought, -when treating of the systematic relations of Tripedalia (p. 5, Fam. III), -to have recognized the analogy to the extent of saying that marginal -lobes may not be completely absent from the velarium of Tripedalia. At -any rate the gelatinous lobes in the case of Chirodropus on the one hand, -and on the other hand the sinuous outline of the margin still mapped out -by the lamella in Chirodropus, Chiropsalmus and Tripedalia, are certainly -very suggestive of an ancestral Cubomedusa in which there was no -velarium, but sixteen free marginal lobes instead. Two more indications -favor slightly the same view. In both Charybdea and Tripedalia a small -notch is seen in the edge of the velarium in the perradius (Fig. 44). Its -constancy suggests that it may not be a chance or meaningless feature. -The second point is the small size of the two marginal pockets adjoining -the perradius. These are in the position of the ephyra lobes of the -Discomedusæ, which always lie on either side of each sensory club, and -which do not keep pace with the other marginal lobes in development. In -the Rhizostome jelly-fish especially they are found much smaller than the -other lobes, as will be seen by a glance at such figures as Haeckel’s for -Lychnorhiza (System, Taf. XXXIV Fig. 2), or for Archirhiza (Taf. XXXVI, -Fig. 5), or Hesse’s figure of the margin of Rhizostoma Cuvieri (’95, -Taf. XXII, Fig. 22). The resemblance between such margins and that of -Tripedalia (Fig. 44), with its simple, unbranched velar canals, is very -suggestive. On the other hand it must be remembered that in considering -the vascular lamellæ of the internal system we found the indication -pointing rather more to Hydromedusan affinities than to any other. -Charybdea throws no light on the question, since it has no marginal lobes -on the velarium and the marginal pockets end strictly at the margin, so -that the only diverticula of the gastro-vascular system in the velarium -are the velar canals. - -Before leaving the subject of marginal lobes and pockets I must answer -a possible objection that may occur to some careful reader. It may seem -that I am wrong in holding that there are two marginal pockets in each -octant instead of three, that just as there is one velar canal from -each of the smaller perradial pockets (_mp´_, Fig. 44), so each prong -of the forked larger pocket (_mp_), since it is continued into a velar -canal, ought to be called a marginal pocket likewise, the whole number -of marginal pockets then being twenty-four instead of sixteen. Such a -revision of the terminology would not be without some reason in its -favor, and perhaps a study of more forms would show it to be correct. -But for the present, at any rate, it seemed to me best to abide by the -analogy of Chiropsalmus, in which the peripheral edge of the larger -marginal pocket in each octant is not bow-shaped, but runs parallel to -the edge of the velarium. A revision of the terminology of the marginal -pockets such as implied in the suggestion above would also give rise to -complications when applied to Charybdea, since the latter has no marginal -pockets in the velarium. - -As to the functions of the vascular lamellæ, there is too little known to -say much. It is rather improbable that structures retained so definitely -should be mere scaffolding left over from a previous stage of usefulness. -Claus has found in Chrysaora that the lamellæ form a kind of capillary -network in communication with the gastro-vascular system, and he with -others supports the view that they perform an accessory function in -the nutrition of the tissues they penetrate. Upon this point I have no -observations of my own to add. - -The marginal vascular lamella is regarded by Claus as perhaps the -vestige of a circular canal around the bell margin. On this subject, -too, I have nothing to add. A lamella of endoderm that connects directly -with the ectoderm of the surface along its whole course is a structure -whose meaning I am wholly unable to understand or even to guess at. A -similar lamella is described by Hesse (’95, p. 430) as occurring in the -ephyra lobes of his Rhizostoma, and he mentions Eimer as the first to -discover this structure, probably meaning the first to discover it in the -Discomedusæ. Whether the lamella is found all around the margin is not -stated. Hesse refers it to the ephyra, and remarks that the investigation -of it in the ephyra would undoubtedly give interesting results. - -I will close this part upon the vascular lamellæ with a very pertinent -suggestion made by Professor Brooks to the effect that the usual way -of speaking of the sensory clubs as having moved up from the margin is -looking at the matter in the wrong way. The level of the sensory clubs -undoubtedly represents the original margin, which elsewhere has grown -down and away from its former level, leaving the sensory clubs like -floatage stranded at high-tide mark. Only in this way can the lamella of -the sensory niche have any meaning. - - -B: THE NERVOUS SYSTEM. - -The nervous system of the Cubomedusæ is the most highly developed that is -found in any of the jelly-fishes. If the position of the group among the -Acraspeda is established, it alone is ample to prove that the Hertwigs -had not sufficient evidence when they stated in their monograph on the -nervous system of the Medusæ (’78) that the Acraspeda show a much lower -nervous organization than the Craspedota. - -The system naturally groups itself under three heads, the nerve ring, the -sensory clubs, and the motor plexus of fibres and ganglia that underlies -the epithelium of the subumbrella. The general relations of the nerve -ring and of the sensory clubs have been given before in the description -of Charybdea Xaymacana, so that we may pass at once to the consideration -of the finer details of the nervous tissues. - -In the structure of the nerve ring I have found myself unable to come -to the same results as those given by Claus, who so far as I know is -the only one that has studied the nerve with special reference to its -histology. Our difference amounts to this, that he finds two distinct -types of cells in the epithelium of the nerve, sensory and supporting, -which would make it a receiving as well as transmitting organ, while I -have not been able to demonstrate satisfactorily the sensory cells, and, -therefore, so far as my own observation is concerned, I am disposed to -attribute to the nerve simply the function of conducting impulses. I do -not know just how much weight to assign to my inability to find evidence -in my sections of the sensory type of cells. Eimer (mentioned by Hesse, -’95, p. 420), the Hertwigs (’78) and Claus (’78) have independently -discovered the two types in one medusa or another, and the Hertwigs, -at least, have demonstrated them by macerated preparations. So far as -Charybdea is concerned, however, Claus had only preserved material and -had to rely upon sections, as have I, since the material which I had -preserved with especial reference to maceration did not turn out well. -The results that we get from sections vary enough for me to believe -that Claus interpreted his sections very much by analogy with other -forms--as indeed, is suggested by his own words (’78, p. 22): “Da es -mir nicht geglückt ist die durch die längere Conservirung in Weingeist -fest vereinigten Elemente zu isoliren, habe ich das muthmassliche -Verhältniss beider Elemente nach Analogie der mir für die Acalephen -bekannt gewordenen Verhältnisse, welche O. und R. Hertwig so schön auch -am Nervenring der Carmarina zur Darstellung gebracht haben, zu ergänzen -versucht.” There can be no doubt of our having the same structures to -deal with, for C. Xaymacana is so much like C. marsupialis as to be -perhaps more worthy of being called a variety of the latter than a -distinct species. - -The structure of the nerve as I conceive it is given in Figs. 47 and 48. -The former represents a cross-section, and shows, as others have pointed -out, that the layer of circular muscle fibres (_cm_) is interrupted -by the nerve. It is evident that the tissues which elsewhere on the -subumbrella were differentiated into muscle epithelium and muscle fibre -have here become nerve epithelium and nerve fibre, a point that has not -been remarked upon before, so far as I remember, and that may be of -interest in connection with the neuro-muscular theory. The epithelium -of the nerve (_scn_) is seen to be made up of cells whose inner ends -narrow down into a kind of stalk or process that runs to the gelatine -of the supporting lamella (_gs_) and there joins a little cone of the -gelatine that juts out to meet it. The cells are smaller in general -than those that overlie the muscle layer, especially on the two lateral -margins of the nerve, where they are more crowded together and overarch -the nerve-fibres. The fibres are seen in cross-section between the -processes of the cells. They apparently must lie imbedded in some -clear, watery fluid that does not show in the preserved material. The -processes of the epithelial cells give the fibres the appearance of lying -in alveoli, or being divided into strands, and one of these strands -(_ax_) is always discernible among the others by reason of its more -numerous or finer or more compactly massed fibres. This is the “axis” of -Claus. Here and there in its course appear ganglion cells having their -long axis in the longitudinal direction of the nerve. Elsewhere, in -the nerve as well, and usually nearer to the surface, are found other -ganglion cells, mostly bipolar, some multipolar, which are readily -distinguishable from those of the axis by the fact that their long axis -lies across the nerve. One of these cells is shown in the figure (_gc_). -Here and there in the epithelium alongside the nerve are found mucous -cells (_mc_), distinguished by their clear contents and by the small -exhausted-appearing nucleus at the base with a few threads of protoplasm. - -In Fig. 48 I have tried to represent the structure of the nerve by means -of a series of five different views such as would be given by focusing at -five successive levels. In the first (1) we have the epithelium of the -nerve (_scn_ in Fig. 47) in surface view, the cells appearing polygonal -in outline, with here and there a mucous cell. In (2) we find a very -slight layer of ganglion cells and fibres having a transverse direction -(_gc_ and _fp_ in Fig. 47). These are continuous with the plexus of -fibres and ganglion cells which lie above the muscle layer all over the -subumbrella, and which represent the motor part of the nervous system. -This connection with the nerve shows how co-ordination is effected. At -the same level are found fibres of the axis also having a longitudinal -direction. In (3) is seen the main body of fibres, divided in the osmic -preparation from which the drawing was made into irregular wavy strands -which are in all probability largely the result of preservation, but are -in part also due to the separation by processes of the epithelial cells, -as was seen in Fig. 47. The axis is seen with one of its longitudinally -directed bipolar ganglion cells; and at the sides the fibres of the -circular muscle of the subumbrella. These show a slanting direction to -the nerve, due to the fact that the nerve, as mentioned before, has a -sinuous course from the margin in interradius to the level of sensory -club in perradius. At the next focus (4) we come to the gelatine of the -subumbrella (_gs_ in Fig. 47), and below this (5) to the larger polygonal -outlines of the endodermal cells of the stomach pocket (_enp_, Fig. 47), -which like the ectoderm show mucous cells at irregular intervals. - -A comparison, now, with Claus’s figures (’78, Taf. II, Figs. 19-21) -will show that, except for the rather unimportant matter of the mucous -cells, which he finds regularly and thickly disposed on each side of -the nerve (’78, Fig. 21), our only essential difference lies in the -matter of sensory cells in the epithelium. His figures show a multitude -of spindle-shaped sensory cells whose central ends are continued in -processes that bend around into the mass of fibres of the nerve. In -his Fig. 20 a relatively small number of nuclei, just one-third as -many, are seen attached nearer to the surface, which represent the -supporting cells. The plan of structure (as shown in his Fig. 20) is an -alternation of (1) supporting cells offering a broad peripheral end to -the surface and having the central end continued as a supporting fibre -to the gelatinous lamella, and (2) spindle-shaped sensory cells with -nuclei at a lower level, which send their peripheral process up between -the supporting cells to the surface, while the central process becomes -continuous with the nerve fibres, often branching into two processes. In -my sections I have not been able to see either a regular alternation of -nuclei at different levels, or central processes which unmistakably bend -round into the nerve fibres. In every case in which I could trace the -central process of a cell clearly it ran to the supporting lamella, and -this whether the nucleus of the cell lay near the surface of the nerve or -deeper down, as in the somewhat spindle-shaped cell seen on the left of -the centre of the nerve in Fig. 47. Of course in many cases the central -process could not be traced in a section, and this leaves room for the -supposition that such were always the sensory cells. From my inability to -demonstrate sensory cells in the nerves of Charybdea, I by no means wish -to deny their existence; for that remains to be proved, or disproved, -by macerations. At any rate, they cannot be so numerous as has been -supposed. The position of the nuclei shows that. - -The epithelium of the nerve is said by Claus to be ciliated. It has been -suggested by Schewiakoff that probably in such cases the sensory cells -bear one long cilium, while the supporting cells have many smaller cilia. -Unfortunately, I made no observations upon the ciliation of the nervous -structures of the living animal, and the traces of cilia that are shown -in preparations of preserved material are a poor basis to speculate much -on. Claus considers the sensory cells of the epithelium of the nerve a -special seat of tactile sensation. - -The way in which the nerve reaches the sensory clubs is interesting. -Under the topic of the vascular lamellæ it was explained that the sensory -clubs and the bottom of the sensory niche from which they spring are -parts of the subumbrella. Fig. 37 reminds at a glance better than any -other one drawing how the bottom or inner wall of the niche is completely -cut off from the exumbrella by vascular lamellæ above and below the -stalk of the club. From this figure, now, it will readily be understood -that the nerve in order to pass to the base of the stalk has simply -to traverse the gelatine of the subumbrella. This fact, which seems -surprising enough at first sight in view of the position of the clubs -on the external surface of the umbrella, was correctly pointed out and -explained by Claus, but one or two figures will serve perhaps to give a -clearer idea of it. - -Fig. 49 is a diagram of the nervous structures in the region of the -sensory niche, as they would be seen on the surface of the subumbrella -turned toward the bell cavity. The outline of the sensory niche as it is -seen through the tissue of the animal is represented by the line _osn_. -The sensory club (_scl_), and its stalk with a conical basal portion are -given by the lightly dotted outline and are also imagined as seen through -the animal. The nerve (_n_), being on the surface of the subumbrella, is -shown as a heavy line describing an arch over the outline of the niche. -In the middle point of the arch is a slight thickening of the nervous -tissue (_rg_) which shows in section a large increase in the number of -ganglion cells, and is the radial ganglion of Claus. The same is seen, -exaggerated in size, in Fig. 12. From it there extends upward a slender -strand of nervous tissue (_rn_), the radial nerve of Claus. In Charybdea -this can be traced but a very short distance. In Tripedalia it is much -more distinct and traceable for a longer distance, and I might say in -passing that this and the sensory organs in the proboscis are the only -differences I have noted between the nervous systems of Tripedalia and -Charybdea. - -Nerve ring, radial ganglion and radial nerve all lie on the bell cavity -surface of the subumbrella. The way, now, in which the nerve ring reaches -the base of the stalk is simply by sending two roots through the gelatine -of the subumbrella to the conical base of the stalk. These roots are seen -in the diagram at _rns_. After passing through the gelatine the roots -come together on the inner side of the base--that is, the side turned -toward the bell cavity--and then pass downwards (_nst_) on the inner side -of the stalk of the club to the mass of nervous tissue at its end. - -This passage of nervous tissue through the gelatine in order to reach the -sensory club is a little hard to grasp at the first, and I have tried -to render it more intelligible by a couple of drawings of sections. -Fig. 50 is a transverse section through the upper part of the region of -the sensory niche, not quite horizontal (_i. e._ parallel with the bell -margin), but slanting so as to lie on the plane of the reference arrow -_x-y_ in Fig. 49. The plane passes just through the top of the niche, and -in two areas has cut through the roof with its epithelium of ectoderm -(_ece_, _ecs_) so that the space of the sensory niche (_sn_) appears. The -vascular lamella of the sensory niche (_vls_) is shown, as in Figs. 13 -and 14, running on each side from the endoderm that lines the canal of -the sensory club (_enc_) to the endoderm of the adjacent stomach pocket -(_enp_). By it the gelatine of the exumbrella is separated from that of -the subumbrella, and one sees that it is only through the latter that -the nerve has to pass in order to reach the base of the sensory club. It -is also seen that one part of the roof of the niche which is cut through -lies outside of the ring of lamella and is therefore lined with ectoderm -of the exumbrella (_ece_) while the other lies within the ring and is -lined with ectoderm of the subumbrella (_ecs_). Owing to the slanting -direction of the cut only the root on one side is cut through. The other -is indicated, however, on the right side of the drawing. In this method -of passage of nerve fibres, together with the accompanying ganglion -cells, directly through the gelatine to the stalk of the sensory club my -work is only confirmation and explanation of Claus. - -Fig. 51 is a vertical section through the base of the stalk in the plane -of the reference arrow _w-z_ in Fig. 49, and therefore passing through -one of the roots of the nerve of the stalk. Here again the region is seen -to be cut off from the exumbrella by the vascular lamella of the sensory -niche (_vls_), and the nerve is seen passing through the gelatine of -the subumbrella from the surface of the bell cavity (_sc_) to the base -of the stalk hanging in the sensory niche (_sn_). One of the ganglion -cells (_gc_) that accompany the nerve is seen to have two nuclei, a not -infrequent occurrence which has been pointed out by others. - -The same figure shows that the axis (_ax_) of the nerve has penetrated -the gelatine with the other fibres. Here at the base of the stalk it -takes a horizontal course and becomes directly continuous with the -similar structure of the other root, as Wilson, I believe, first pointed -out. This part of the nervous tract which runs horizontally along the -base of the stalk between the two roots (Fig. 49, _rns_) has been -considered by Claus the representative in Charybdea of the upper nerve -ring of the Craspedota, which therefore exists in Charybdea in four -separate portions. Seeing, however, that the region in which it is found -belongs to the subumbrella, the homology seems very doubtful. Moreover, -the fact that the axis of the nerve ring runs through this outer portion, -instead of remaining on the inner surface of the subumbrella and passing -to the radial ganglion, rather indicates that the outer portion is part -of the original course of the nerve ring, while the portion that remains -on the inner surface is perhaps a later formation. - -A very interesting feature of the nervous system occurs in the same -region in the form of a tract of fibres underlying the endoderm, and -separated from the other fibres by the gelatine of the supporting -lamella. It is seen in vertical section in Fig. 52 (_enf_), which -is a section through the base of the stalk in just about its median -plane, and, therefore, to one side of the arrow _w-z_ in Fig. 49 and -the corresponding drawing, Fig. 51. In cross-section it is represented -also in Fig. 50 (_enf_). It varies in size and prominence very much -in different specimens. Fig. 52 is a camera drawing of it in the case -that showed it most developed. Ganglion cells are found in it, but -comparatively infrequently. In some cases the tract itself can hardly -be found with certainty. Hesse has described in a Rhizostome a much -more highly developed tract in a corresponding position on the base of -the marginal body. Fibres from the “outer sensory pit” pass through the -gelatine to the sub-endodermal tract, which is described as surrounding -the epithelium of the canal of the marginal body like a collar and is -most thickly developed on the under surface of the canal, at the place -that just corresponds with the point where, and where only, I find the -tract in Charybdea. Hesse thinks that fibres then pass from this region -to the nervous epithelium of the “inner sensory pit” lying underneath -the base of the marginal body, which contains a rich supply of ganglion -cells and is considered by him to be the centre of the nervous system of -the medusa. A close comparison cannot be drawn with Charybdea in this -matter, however, since Charybdea has nothing to correspond with the -“outer” and “inner” sensory pits. Moreover, the endodermal tract is not -found encircling the canal of the sensory club, nor could I trace fibres -passing from it through the supporting lamella into the fibres of the -nerves. - -Claus has figured (’78, Taf. V, Fig. 45, _Fb_) a small bundle of fibres -in the stock of the sensory club lying between the endoderm cells of -the canal and the supporting lamella. The same bundle is found in both -Charybdea and Tripedalia and can be traced in cross-sections up the -stalk to a point which must correspond with that at which the endodermal -tract is seen in Fig. 52. Downwards it can be traced only as far as the -entrance of the stalk into the knob of the club where it invariably -becomes lost to view. According to Hesse (’95, p. 427) Schäfer found -under the endoderm cells of the whole stalk of the marginal body a -fibrous layer like that under the endoderm cells which he refers to -slender processes from the cells of the crystalline sac. Although Hesse, -as we have seen, finds the layer more limited in extent than Schäfer -gives it, and does not trace it to the same source, the observation of -Schäfer seems to me worthy of mention here, inasmuch as the trend of -the fibrous bundle under the endoderm cells of the stalk in Charybdea -and Tripedalia suggests quite strongly that the fibres come from the -crystalline sac, as Schäfer thought to be the case in his medusa. - -Besides the radial ganglion situated in the course of the nerve ring at -its four perradial points there are four other similar ganglia on the -subumbrella. These lie in the interradii, at the four lowermost points -of the nerve’s course, and undoubtedly send off nerves into the pedalia -at whose bases they are situated. F. Müller (’59), whose work was not -accessible to me, is quoted by Claus as recording two ganglia opposite -the base of each pedalium which gave off a great number of nerves partly -into the velarium, partly into the tentacles. Claus observed nothing of -the kind in Charybdea and states that even the interradial ganglia do not -exist. - -That they do, however, is shown without doubt in sections of both C. -Xaymacana and Tripedalia, but nerves to the velarium or to the tentacles -I was unable to find. - -On the two sides of each frenulum and of each suspensorium are found -subepithelial ganglion cells in greater numbers than elsewhere on the -subumbrella, and I am inclined to ascribe to them also the importance -of special ganglia controlling the musculature of the frenula and -suspensoria. Certainly such ganglia would not be out of place. - -It has been mentioned that the greater prominence of the radial nerve and -the possession of special sensory organs in the proboscis were the only -points of difference I had noted between the nervous systems of Charybdea -and Tripedalia. These sensory organs remain to be described. They are -simple ciliated cysts containing a concretionary mass, and are situated -in the gelatine of the proboscis, irregularly disposed of at any level, -from the lips to the beginning of the stomach, and in any radius. In one -series of the adult animal fifteen were counted, of which seven were -situated about interradially, four perradially, two adradially and two -subradially. In another, twenty-one were counted, twelve in the perradii -and nine situated between the sub-and perradii. The one shown in Fig. 24 -is in the perradial position, often seen. In the sections of the very -young Tripedalia in which the vascular lamella had not reached the adult -condition the sensory organs of the proboscis were not found, although -the sensory clubs showed practically no difference from the adult. -Their structure is very simple--merely a round or oval sac lined with -ciliated cells which bear up and keep in constant motion an irregular -coarsely granular concretion. Fig. 53 is a sketch made in Jamaica from -the living specimen. Sections were somewhat disappointing in that they -added but little. Fig. 55 was drawn to show that now and then a mucous -cell (_mc_) is found among the other cells of the sensory epithelium. An -irregular-shaped mass (_rc_) was always found inside the cysts as the -organic remains of the concretion. It gave no trace of cellular structure -and offered no evidence whether the concretion was the product of one or -few or of all the cells of the cyst. The latter would be unique among -the medusæ. Even if the otocyst is the result of the activity of only -one or a few cells, it is, so far as I know, the only case known for the -jelly-fish of a free, unsuspended concretion. - -As to whether the cysts are of ectodermal or endodermal origin could not -be determined, but there was some evidence in favor of the latter. Fig. -56 is a drawing of one seen in optical section in a whole mount of part -of a proboscis, and shows a definite connection with the endoderm of the -proboscis. This was the only case when such connection was satisfactorily -established, but in sections it was not uncommon to find what seemed to -be the remains of the broken stalk, as in Fig. 54 (_rs?_). No connection -could be traced between the cysts and any other part of the nervous -system. As to function, the idea that they serve to give perception of -space relations suggests itself as readily as any other hypothesis. - -We come now to the consideration of the terminal knob of the clubs, the -sensory portion proper. A complete and detailed account of the complex -structure of these organs would fill many pages and involve much useless -repetition. Claus (’78) has described them with accuracy, but not in -great detail, and since then Schewiakoff (’89) has given a careful -general description and has supplemented Claus’s work by observations -upon the finer structure made with the aid of more recent technique. It -seems in place for me, therefore, to give in the briefest possible way a -general idea of their structure, and to pass then at once to the points -in which my work has led me to different conclusions from those of Claus -and Schewiakoff. In brief, then, the knob of the sensory club consists -of a thick, complex mass of nerve fibres, more or less imbedded in which -lie the special sensory organs, surrounding the ampulla-like terminal -enlargement of the canal. The surface between the special organs is -covered with less specialized sensory epithelium. The sensory organs are -seven in number. Of these, four are simple invaginations of the surface -epithelium arranged in two pairs symmetrically to the median line in the -proximal end of the knob (the end where the stalk enters) and having -pigment developed in the cells so invaginated, while the space of the -invagination is filled with a gelatinous refracting secretion. These -are considered simple eyes. Two more of the organs are complex eyes -situated on the median line of the inner surface of the knob, the upper -one smaller than the lower, but having almost exactly the same structure. -Each has a cellular lens over which extends a superficial, corneal layer -of cells; below the lens a refractive “vitreous body”; and below this -a retina with pigmented cells. The seventh organ is the crystalline -sac, which lies almost at the end of the knob opposite to the stalk and -contains a large concretion. In view of the fact that the sensory clubs -_in toto_ have been abundantly figured by Claus and Schewiakoff, it is -my intention to give but one simple figure of the general relations, and -I justify that one in that it was made from the fresh material. Fig. -57 is a camera sketch of the outlines given by a sensory club seen in -optical section from the side. The smaller upper and the larger lower -complex eyes which are situated on the mid-line, are seen in profile, -while the two small simple eyes give the outlines that they would in a -surface view of their side of the knob. Of course it is understood that -two similar ones would appear on the other side, since the four simple -eyes are symmetrically paired on either side of the mid-line. The sketch -seems to show at least this much, that even in the living state the lens -of the larger eye projects out beyond the other contours of the surface, -so that the marked convexity ascribed to it in descriptions is not to be -attributed to the preservation. - -It is in reference to the structure of the retina and vitreous body of -the complex eyes that I have found myself unable to come to the same -conclusions as Claus and Schewiakoff. Since the work of the latter goes -much further into the detail of the subject than does Claus’s paper, it -will be sufficient for me to compare my results simply with those of -Schewiakoff. - -The latter finds that the retina is composed of two kinds of cells, -corresponding to the supporting and sensory cells referred to in the -description of the nerve ring. These he figures (’89, Taf. II, Figs. -12 and 13) as alternating regularly. The two kinds of cells differ as -follows: - -(1) Shape. The supporting cells like those referred to before, are -cone-shaped, having a proximal fibrous process that runs into the -underlying stratum of nerve fibres, and on the surface of the retina a -broad distal pigmented termination. The sensory cells are spindle-shaped, -the proximal processes becoming continuous with fibres of the underlying -nervous mass, while the distal process runs up to the surface of the -retina (the part toward the lens) in between the ends of the supporting -cell. The two kinds of cells are accordingly designated as pigment and -visual. - -(2) Position of nucleus. This comes in as a corollary of the shape. -The nuclei of the visual cells lie in the enlarged central part of the -spindle-shape, and, therefore, at a lower level than the nuclei of the -alternating pigment cells. - -(3) Processes in the vitreous body. The distal processes of the -spindle-shaped visual cells are continued through the vitreous body to -the cells of the lens as rod-like visual fibres which lie in canals in -the (supposedly) homogeneous vitreous body. The pigment cells on the -other hand have no fibres passing from them through the vitreous body, -but in the latter are situated cone-shaped masses of pigment whose bases -rest upon the broad ends of the pigment cells without, however, being a -part of the cell. - -(4) Pigment. The distal ends of the pigment cells in the retina are -strongly pigmented, as the name implies. The processes of the visual -cells, which alternate with these, are pigmented likewise, but the -pigment is not so abundant and lies in the periphery of the cell body, -leaving free a highly refracting central axis. - -If the relation of these cells to each other has been made sufficiently -clear, it will be understood that, in accordance with Schewiakoff’s -scheme of the structure, sections that cut the retinal cells transversely -give very different appearances at different levels. A section through -the very tops of the retinal cells, that is, the last section of the -retina before striking the vitreous body, would show large polygonal -areas of heavy pigment (the ends of the pigment cells), in between which -would lie the much smaller, less pigmented, highly refracting ends of the -visual cells (’89, Taf. II, Fig. 19). A section lower down in the retina, -that is, more toward the centre of the club, would strike the low-lying -enlarged central portion of the visual cells with their contained nuclei, -and the smaller, proximal ends of the pigment cells. It would, therefore, -give the reverse appearance from the preceding section, namely, that of -large unpigmented (or but slightly pigmented) areas (the swollen bodies -and nuclei of the spindle-shaped cells), and in between them smaller -pigmented areas, the ends of the proximally tapering pigment cells -(’89, Taf. II, Fig. 20). A section on the other side of the one first -described, that is, one of the first through the vitreous body, would -show pigment areas of the same size as the large ends of the pigment -cells (the cone-shaped streaks of pigment in the vitreous body which -according to Schewiakoff are associated with the pigment cell), and in -between them the cross-sections of the rod-like processes from the visual -cells, lying in canals in the clear homogeneous ground-substance of the -vitreous body (’89, Taf. II, Fig. 18). - -Let me give a resumé of Schewiakoff’s conception of the structure of the -retina. - -a. There is an alternation of pigment and visual cells, the nuclei of -the spindle-shaped visual cells lying at a lower level than those of the -cone-shaped pigment cells. - -b. From the visual cells extend rod-like processes into the vitreous -body, lying in canals in the latter. - -c. In the vitreous body a cone-shaped streak of pigment overlies each -pigment cell of the retina, which is not a part of that cell. - -d. Apart from these pigment streaks and the rod-like processes of the -visual cells the vitreous body is structureless, probably a secretion of -the pigment cells. - -My own work, now, has led me to a different conception, so that my -conclusions on the same points would be as follows: - -a. There is not good evidence of an alternation of cone-shaped pigment -cells and spindle-shaped visual cells, with the nuclei of the latter at a -lower level than those of the former. - -b. From some of the retinal cells otherwise not distinguished, there -extend rod-like processes into the vitreous body, such as described by -Schewiakoff. - -c. The cone-shaped streaks of pigment in the vitreous body belong to the -underlying pigment cells, in fact are direct continuations of them, and -at their distal ends they are prolonged into fibrous processes lying in -canals of the vitreous body exactly like the visual fibres of Schewiakoff. - -d. The vitreous body is not a homogeneous secretion, but is composed of -prisms of refracting substance, each with a denser central fibre. - -Let us go over these four points in detail. - -(a) As to the first, the question whether there is an alternation of -pigment and visual cells, I am not prepared as yet to make a positive -statement, since my not seeing both kinds as they are described has -little evidential value against the fact that Claus and Schewiakoff both -claim to have seen them. Perhaps proof could be obtained one way or the -other by maceration of fresh or of specially prepared material, which -none of us had. My evidence for not confirming alternation rests wholly -upon sections. Fig. 58 represents a radial section through part of the -larger eye of Charybdea, made from an osmic preparation which in this -case showed two advantages over the material fixed in corrosive-acetic -(usually by all odds the best), namely, that the vitreous body (_vb_) was -not shrunken away from the retinal cells, as almost invariably happens, -and that the retinal cells were contracted apart from one another in some -places in such a way as to be almost equal to a macerated preparation. -Now, in the figure it is seen that there is an apparent alternation of -two kinds of cells, more regular than I usually find, but the ones that -are undoubtedly the pigment cells of Schewiakoff are the ones that show -the fibrous processes like his visual cells, and the pigment streaks -in the vitreous body are seen to be integral parts of the cells, not -cone-shaped masses lying in the vitreous body, merely associated with -the pigment cells. If these _are_ the pigment cells of Schewiakoff, -the shorter cells in between must be his visual cells, yet they can by -no means be said to conform to a spindle-shaped type, nor are their -nuclei always at a lower level than (that is, internal to) those of -the pigment cells. If the long cells with the fibres are, on the other -hand, considered the visual cells of Schewiakoff, then again we find -nonconformity to a spindle-shaped type, and nuclei not always at a lower -level. The matter of alternation of nuclei at different levels seems -to me any way too slight a distinction upon which to base a difference -in function. It is a necessary mechanical consequence of the crowding -together of many cells on one surface. And in many cases in perfectly -radial sections through the retina I find the nuclei fewer in number and -arranged in very nearly a single level. The retina of the smaller eye -represented in Fig. 69 shows this. In sections further along in the same -series the nuclei are found at different levels, due without doubt to the -slanting cut. - -[Illustration: [Dr. Conant did not complete Fig. 72, and the -accompanying outline of Fig. 7 of Schewiakoff’s memoir (Beiträge zur -Kenntnis des Acalephenauges, Morph. Jahrb., Bd. XV, H. 1) has been -substituted.--EDITOR.] - -EXPLANATION OF LETTERS IN TEXT FIGURE.--_C_--concretion cavity; -_CO_--cornea; _CP_--capsule of lens; _CSC_--cavity of sensory club; -_EC_--ectoderm; _EN_--endoderm; _ENC_--endoderm of sensory club; -_L_--lens; _NC_--network cells; _NF_--nerve fibres; _RT_--retina; -_SLA_--supporting lamella; _VF_--vitreous body.] - -Fig. 72 is a horizontal section through the large eye, and shows that -here, too, when the sections pass through the eye just radially, the -nuclei are not found at different levels sufficiently definite to suggest -two kinds of cells. - -In the inner corner of the retina in the same figure (69) are seen cells -without pigment which show nuclei undoubtedly at different levels. -These cells in this position are a regular feature in the retina of the -smaller eye. Schewiakoff considers them purely visual, because of the -lack of pigment. In so doing it seems to me he forgets his own standard -for discriminating between pigment and visual cells. The pigment cells -of the retina, according to him, are the same thing as the cone-shaped -supporting cells found elsewhere in the nervous epithelium, and are, -therefore, distinguished from the visual cells primarily by shape and by -position of nucleus, secondarily by the greater development of pigment. -When on the ground of pigmentation alone he calls the cells in the corner -of the retina visual, he judges them by only the second test, and in -so doing virtually admits, as it seems to me, that shape of cell and -position of nucleus are matters of no great moment. His own standards -place him in a dilemma. If on the other hand he judges by the lack of -pigment, the cells are visual; if by shape of cell and position of -nucleus, they are both visual and pigment cells without the pigment or -supporting cells. What use there would be for simple unpigmented cells in -one limited region of the retina is hard to see, so he naturally takes -the other horn of the dilemma and calls them visual because they have -little or no pigment. - -The distinction, then, between pigment and visual cells is brought down -to one of pigmentation only. Schewiakoff’s test for this is that in the -visual cells “Das Pigment durchsetzt aber nicht das ganze Protoplasma des -centralen Zellenabschnittes, sondern ist auf seine Oberfläche beschrankt -(Fig. 19, _sz_), so dass der innere, axiale, stark lichtbrechende Theil -vollkommen frei von demselben ist.” (’89, p. 37.) That is, in a section -through the ends of the retinal cells each pigment cell will appear as a -uniformly pigmented area, while each visual cell will appear as a light, -strongly refracting spot with a ring of pigment around its periphery. -This is the arrangement given in his Fig. 19. - -An arrangement so definite ought to be easily made out in sections, -yet I have not been able to find it so. My sections show considerable -difference in the amount of pigmentation even in material preserved with -the same killing agent. If the retina is heavily pigmented the ends -of the cells have the appearance shown in Fig. 62, which represents -a portion of a cross-section. The ends are seen as clearly defined -polygonal areas differing among themselves in size, but not showing -two types of size, or two kinds of pigmentation, the one uniform, the -other a ring of pigment around a highly refracting central portion. If -the retina is but slightly pigmented--and some were so light as to make -depigmentation unnecessary--a difference is seen in the pigment, as -shown in Fig. 63, but in no case were areas found that showed a highly -refracting centre surrounded by a ring of pigment. (The unexplained -structures in Fig. 63 will be referred to a little later.) - -Figures 59-62 are a series of four successive sections drawn with the -camera lucida for comparison with Schewiakoff’s Figs. 20 and 19, and to -show that the presence of two types of cells plainly marked within the -retina by the position of the nuclei at different levels is at least not -clearly demonstrated. Only the nuclei are drawn, since the cell bodies -are not easily distinguished from the surrounding fibres. The eye is the -same as that from which Fig. 72 was made. Fig. 59 shows a relatively -small number of nuclei of slightly larger size than usual. These I take -for two reasons to be nuclei of the ganglion cells that are found in the -fibres at the base of the retinal cells (Figs. 58, _gc_, 69 and 72). They -are the first nuclei struck in tracing sections toward the retina, and -in the series from which Fig. 58 was taken similar nuclei appeared in -both transverse and radial cuts through the retina stained brightly and -clearly with hæmatoxylin, whereas the nuclei of the retinal cells proper -were stained a diffuse brownish-yellow from pigment that had evidently -gone into solution. Fig. 60 shows the closely aggregated, smaller nuclei -of the retinal cells surrounded by the nuclei of the outlying ganglion -cells. Schewiakoff’s corresponding drawing (’89, Fig. 20) shows at this -level a definite alternation of the bodies and nuclei of unpigmented -visual cells, with the smaller, pigmented, proximal processes of the -pigment cells. In the next section (Fig. 61) the pigmented ends of a -few of the cells have been struck, and the following section (Fig. 62) -shows that, in this heavily pigmented specimen at least, there is no good -evidence within the retina itself of two kinds of cells, so that it is -apparent that at any rate we cannot accept Schewiakoff’s conception of -the structure. - -(b) Yet the fibres that Schewiakoff observed and associated with special -visual cells occur beyond question. Fig. 64 is a drawing of the first -cut through the vitreous body of Charybdea, and in among the sections of -the pigment streaks are seen sections of processes lying within clear -spaces exactly as Schewiakoff figures his visual fibres (’89, Taf. II, -Fig. 18). That the fibres occur is indisputable, but as to the cells to -which they belong I can say nothing except that from such evidence as -I have given in the preceding paragraph I conclude that they come from -pigmented retinal cells of not very different type within the retina from -the others, if different at all. - -(c) On the third point, that the pigment streaks in the vitreous body -belong to underlying cells and are continued distally into fibrous -processes like the visual fibres of Schewiakoff, the evidence is -decisive. Fig. 58 has already shown it, and if this were not enough, a -case of unusual stoutness of the fibres drawn in Fig. 67 is conclusive. -The preparation from which the section is taken was one preserved with -corrosive-acetic, and I have drawn the outlines with the camera in -order to avoid exaggeration of the fibres as far as possible, and also -to show the shrinkage of the vitreous body (_vb_). It is the shrinkage -of the vitreous body that makes it so difficult to determine the exact -relation of structures seen in the vitreous body to the retina. The -fibrous processes run through the vitreous body to the “capsule” of the -lens (_cp_) (see also Fig. 72), a layer of homogeneous substance much -resembling that of the vitreous body, which is classed as a part of -the vitreous body, but usually in the shrinking adheres to the lens. -The capsule is therefore regarded by Schewiakoff as a secretion of the -lens cells. Some fibres were found by him to have the appearance of -branching upon reaching the surface of the capsule, others of passing -through it and of seemingly ending among the cells of the lens. The -same appearances were given in my sections. It is altogether impossible -in the distal portion of the vitreous body to distinguish between the -fibres of Schewiakoff and those that come from the long pigment cells. -(Figs. 64-66 represent the appearance of the vitreous body at successive -levels, and are from the same series of sections as Figs. 59-62 and 72.) -In Fig. 64 the sections of the processes that Schewiakoff calls visual -are easily distinguished from the sections of the long pigment cells. -In Fig. 65, which is two or three sections nearer the lens, the pigment -cells are shown by their cross-sections to be tapering down, and in Fig. -66, nearer still to the lens, the two kinds of processes are no longer -to be distinguished from each other. In a few cases I have found pigment -in a fibre which but for this would be called one of the visual fibres -of Schewiakoff. Such considerations as these, the similar appearance in -cross-section, the finding of pigment in a few cases, and the inability -to trace to any readily distinguished special type of retinal cell, make -me wonder whether the visual fibres of Schewiakoff are anything more than -the distal processes of pigment cells, into which the pigment granules -happened not to be produced at the moment of fixation. - -Fig. 63, however, where the retina was only slightly pigmented, rather -speaks against this view, for the number of darkly pigmented areas seen -here (which are shown beyond question by radial sections to belong to the -long pigment cells) is not great enough to account for the number of both -pigment areas and visual fibres of Schewiakoff seen in such a section as -Fig. 64. This would throw the visual fibres of Schewiakoff back upon some -of the slightly pigmented cells of Fig. 63, otherwise not distinguished. -I think the question cannot be settled without the maceration of fresh -material, and experiments upon eyes killed in the light and in the dark. - -In such cases as that of Fig. 63 it would seem conclusively shown that -the long pigment cells must belong to a different type from the short, -but as I have already said I can find no regularity in either their shape -or in the position of their nuclei. And on the other hand Fig. 58 shows -that the reverse relation may obtain and the long cells be less deeply -pigmented on the edge of the retina than their shorter neighbors, so -that it looks as if all the short cells had to do was to project half -their pigment out into the vitreous body in order to become exactly like -the long ones. This they could do if, as is possibly the case, they -are prolonged into “visual fibres” of Schewiakoff that have escaped -observation and so do not appear in the drawing. - -Fig. 58 shows one more thing that is worthy of remark in passing. In the -preparation in which the vitreous body (at this point at any rate) was -not shrunken away from the retina, the fibre from each long pigment cell -does not lie in a clearly defined space or “canal,” such as is usually -described as a constant structure of the vitreous body. Very likely these -canals are formed only by shrinkage around the fibres, and the irregular -shape of the spaces around the three fibres in Fig. 67 rather bears out -the same supposition. - -As to the structure of the vitreous body, apart from the fibres and -pigment streaks already mentioned, I find it to be made up of prisms -extending from retina to capsule of lens, each containing a central -axis or fibre. Fig. 64 shows that the space around the pigment areas -and “visual fibres,” instead of being homogeneous, is wholly filled -with the polygonal cross-sections of these prisms. In Charybdea they -are generally more difficult to perceive than in my best material of -Tripedalia which was killed in acetic acid. In this the polygonal areas -stood apart from each other more plainly. Curiously enough I have been -unable to demonstrate in Tripedalia the “visual fibres” of Schewiakoff. -Here and there were found spaces that at first sight reminded of them -(Fig. 69, _sh_), but they contained no central fibre, and were probably -due to shrinkage. The polygonal areas themselves, however, often -contained a clear spot in the centre, at one side of which would be found -the cross-section of the fibre, as is shown in many cases in Fig. 68. -The clear spot is here undoubtedly due to shrinkage of the gelatinous -substance of the prism. - -I think that these prisms and fibres are the direct continuations of -retinal cells. In a section such as that drawn in Fig. 63, which takes -just the very tops of the cells of a slightly pigmented retina, in the -centre of the section just grazing the space that lies between the retina -and the shrunken vitreous body, most of the cells toward the middle -(where especially the extreme tips are taken) show in their centres a -dot exactly corresponding to the dots in the polygonal areas of the -vitreous body. In the exact middle of the section, where only the cell -walls appear, slightly indicated, a dot is seen in each case. The size -and shape of the ends of the cells correspond with those of the polygonal -areas in the vitreous body, and I do not doubt that the latter are -continuations of the former. The vitreous body, then, instead of being -homogeneous, is composed of the clear highly refracting outer ends of -retinal cells. The assumption lies near that these are the true visual -rods, but of course it is assumption only. - -To give a brief review, the points in which my conclusions differ from -those of Schewiakoff are as follows: I find (1) that the long pigment -streaks are parts of retinal cells continued into processes like his -visual rods; (2) that the vitreous body is composed of prisms with -central fibres proceeding from retinal cells; (3) that I am unable to get -satisfactory evidence of two types of cell distinguishable within the -retina, and at any rate find considerable evidence against the two types -he distinguishes. - -These results are not wholly satisfactory, for they leave us with three -kinds of fibrous processes in the vitreous body which for the present -we are unable to trace to three, or even two distinguishable types -of cell in the retina. It would be more pleasing if we could confirm -Schewiakoff’s simple conception of the structure, with its one set of -visual rods in the vitreous body referable to a clearly marked type of -sensory cells in the retina, but I think the evidence that has been -brought up justifies the conclusion that in some respects he saw too -much, in other respects too little. This is not to be wondered at, -since his material, to judge from a single statement, consisted of but -twelve marginal bodies, and, moreover, the work on Charybdea forms -but one portion of a paper that is excellent for the clearness of its -descriptions and illustrations. - -Before leaving the subject I must mention that Wilson suggested from -his observations on Chiropsalmus that the vitreous body had a prismatic -structure, but he was probably mistaken when he thought he found evidence -of nuclei in it. Claus says that the retina is composed of pigment and -rod cells alternating, and Wilson agrees with him, but under a sketch -of a sense cell from the nerve he makes the express statement “not very -well preserved.” It seems very probable, therefore, that he followed -Claus’s interpretation rather than independent observations, and Claus -interpreted his results very much by analogy of what had been found in -other forms. - -The smaller complex eye which is represented in Fig. 69 agrees in -structure very closely with the larger. The chief differences are that -sections do not show pigment extending into the vitreous body, that there -is no “capsule” to the lens, and that the lens seems to be supported by -a kind of stalk formed by a thickening of gelatine of the supporting -lamella (_sl_). The gelatinous thickening lies between the lens and an -outgrowth of endodermal cells (_en_) from the canal of the club. This -outgrowth is a constant feature, figured by Claus and Schewiakoff for -Charybdea, and by Wilson for Chiropsalmus, and found in Tripedalia also. -The regularity of its appearance in all three genera leads one to suspect -that it may have some significance not yet understood. - -Just above the smaller eye there lies a mass of cells of peculiar -structure (Fig. 69, _nc_). They are of a rounded polygonal contour, with -a comparatively small circular nucleus in the centre, and are found in -this region only. In and amongst them bundles of fibrous tissue are found -in the sections, which pass from the surface cells to the supporting -lamella. Claus describes the contents of these cells as coarsely granular -protoplasm and says they cannot be taken for ganglion cells. He is -inclined to believe that they play the part of a special supporting -tissue. Schewiakoff, on the other hand, is convinced that they are -ganglion cells, and finds processes passing out from them (’89, Taf. II, -Fig. 22). I find, however, that the cell contours are perfectly regular -and clearly without processes, and it is incomprehensible to me how, -if his material was at all well preserved, he could for a moment have -taken them for the same thing as the big multipolar ganglion cells with -large nucleus and nucleolus which lie in about the same region and were -correctly described and figured by Claus but are not specially mentioned -by Schewiakoff. I cannot agree with Claus, however, that their contents -are composed of coarsely granular protoplasm. That which appears such -by low magnification shows itself under high powers to be a beautiful -network with thickenings at the nodes of the meshes, which is brought -out very plainly by a cytoplasmic stain such as Lyons blue. Around the -nucleus is seen a more or less well-defined clear zone. What the function -of the cell is remains as unknown to me as to Claus and Schewiakoff. - -There is left one more point in reference to the nervous system upon -which I wish to say a word. Claus and Schewiakoff both describe the wall -of the crystalline sac as structureless, formed by the bare supporting -lamella. The credit is due to H. V. Wilson of finding in Chiropsalmus -that it has a special lining of epithelial cells, which he figures as -a continuous, flattened layer. In both Charybdea and Tripedalia I find -traces of the same in nuclei here and there, but whether they are the -remains of a once continuous layer or not the sections do not show -satisfactorily. - -This ends the account of what it seemed worth while to say at present -upon the nervous system. In concluding, the writer wishes to express -his thanks for the help afforded by Dr. Wilson’s notes, in particular -on the subject of the vascular lamellæ, and desires to make especial -acknowledgment of his indebtedness to Professor Brooks, whose -suggestions, based upon many years of experience with the Medusæ, -have been most welcome and helpful, and whose evidences of unfailing -kindliness, both in Jamaica at the time the material was obtained and -in Baltimore when it was being studied in the laboratory, take a most -honored part in the pleasant memories associated with the work. - - -LITERATURE REFERRED TO. - - CLARKE, H. J. ’78. Lucernariæ and their Allies. Washington: - Smithsonian Institution. - - CLAUS, C. ’78. Ueber Charybdea marsupialis. Arb. aus d. Zool. - Inst. d. Univ. Wien, Band II, Heft 2. - - DOFLEIN, F. ’96. Die Eibildung bei Tubularia. Zeitsch. f. wiss. - Zool., Bd. LXII, Heft 1. - - HAECKEL, E. ’79. Das System der Medusen. Jena.--’81. Challenger - Report on the Deep-sea Medusæ. Vol. IV. - - HERTWIG, O. and R. ’78. Das Nervensystem und die Sinnesorgane - der Medusen. Leipzig. - - HESSE, R. ’95. Ueber das Nervensystem und die Sinnesorgane von - Rhizostoma Cuvieri. Zeitschr. f. wiss. Zool., Bd. LX, Heft 3. - - MÜLLER, F. ’59. Zwei neue Quallen von St. Catherina - (Brasilien). Abhandlungen der naturf. Gesellschaft zu Halle. - - SCHEWIAKOFF, W. ’89. Beiträge zur Kenntniss des Acalephenauges. - Morph. Jahrb., Bd. XV, Heft 1. - - WILSON, H. V. Unpublished notes. - - -TABLE OF REFERENCE LETTERS. - - _afr_ = adradial furrow. - - _afr´_ = furrow in Tripedalia that separates perradial from interrad. - regions in lower half of bell. (In Charybdea the same furrow - is directly continuous with _afr_.) - - _ax_ = axis of nerve. - - _c_ = concretion. - - _cc_ = canal underneath _ivl_, connecting the two adjacent marginal - pockets. - - _ccl_ = circular canal. - - _ci_ = cilia. - - _cm_ = circular muscle. - - _co_ = cornea. - - _cp_ = capsule of lens. - - _cs_ = covering scale of niche. - - _csc_ = canal of sensory club. - - _ct_ = canal of tentacle. - - _ct´_ = beginning of canals of lateral tentacles in Tripedalia. - - _ec_ = ectoderm. - - _ece_ = ectoderm of exumbrella. - - _ecs_ = ectoderm of subumbrella. - - _ed_ = distal paired eye. - - _el_ = larger unpaired eye. - - _en_ = endoderm. - - _enc_ = endoderm of sensory club. - - _enf_ = tract of nerve fibres underlying endoderm. - - _enfl_ = endoderm of floor of stomach. - - _enp_ = endoderm of stomach pockets. - - _enr_ = endoderm of roof of stomach. - - _ens_ = endoderm of stomach. - - _ep_ = proximal paired eye. - - _es_ = smaller unpaired eye. - - _fc_ = funnel leading into canal of sensory clubs. - - _fp_ = fibre from subepithelial plexus of subumbrella. - - _fph_ = filaments of phacellus. - - _frn_ = frenulum. - - _ft_ = funnel-shaped depression in ectoderm axial to base of - tentacle. - - _g_ = gelatine. - - _gc_ = ganglion cell. - - _ge_ = gelatine of exumbrella. - - _go_ = gastric ostium. - - _gs_ = gelatine of subumbrella. - - _hvl_ = horizontal vascular lamella. - - _i_ = interradius. - - _if_ = interradial funnel of bell cavity. - - _ifr_ = interradial furrow. - - _ivl_ = interradial vascular lamella. - - _l_ = lens. - - _lv_ = lip of valve. - - _m_ = bell margin. - - _mc_ = mucous cell. - - _mep_ = mesogonial pocket. - - _mo_ = mouth. - - _mp_ = marginal pocket. - - _mp´_ = smaller marginal pockets, in Tripedalia. - - _mst_ = muscle of stock of sensory club. - - _mt_ = muscle at base of tentacle. - - _n_ = nerve. - - _nc_ = network cells, in sensory club. - - _nf_ = nerve fibres. - - _nm_ = nematocyst. - - _nst_ = nerve of stalk of sensory club. - - _osn_ = outline of sensory niche. - - _p_ = perradius. - - _pe_ = pedalium. - - _ph_ = phacellus. - - _pr_ = proboscis. - - _r_ = reproductive organ. - - _rc_ = remains of concretion. - - _rcl_ = radial canal. - - _rg_ = radial ganglion. - - _rm_ = radial muscle. - - _rn_ = radial nerve. - - _rns_ = root of nerve of sensory club. - - _rs?_ = remains of stalk (?) of sensory organ. - - _rt_ = retina. - - _s_ = stomach. - - _sc_ = bell cavity. - - _scl_ = sensory club. - - _scn_ = supporting cell of nerve. - - _se_ = sensory epithelium. - - _sh_ = shrinkage space. - - _sl_ = stalk of lens. - - _sla_ = supporting lamella. - - _sn_ = sensory niche. - - _so_ = sensory organ in proboscis of Tripedalia. - - _sp_ = stomach pocket. - - _sph_ = stalk of phacellus. - - _ss_ = stalk of sensory organ, in proboscis. - - _st_ = stalk of sensory club. - - _su_ = suspensorium. - - _sub_ = subumbrella. - - _tl_ = lateral tentacle. - - _tm_ = median tentacle. - - _v_ = velarium. - - _va_ = vacuole. - - _vb_ = vitreous body. - - _vc_ = velar canals. - - _ve_ = edge of velarium. - - _vfs_ = visual fibres, according to Schewiakoff. - - _vg_ = valve of gastric ostium. - - _vl_ = vascular lamella. - - _vlc_ = vascular lamella connecting _vls_ with _vlm_. - - _vlm_ = vascular lamella of margin. - - _vls_ = vascular lamella of sensory niche. - - _vlst_ = vascular lamella of sensory niche at base of stalk. - - _wc_ = wandering cells. - - _w-x-y-z_ = successive levels of Figs. 40-43 on Fig. 5. - - -DESCRIPTION OF FIGURES. - -Fig. 1. Charybdea Xaymacana, from one of the four interradial sides. - -Fig. 2. The same from above. - -Fig. 3. The same from below, the four tentacles cut off. - -Fig. 4. The same cut in halves vertically (or radially) through a -perradius. - -Fig. 5. The same out in halves vertically (or radially) through an -interradius. - -Figs. 6-16. Diagrams of horizontal (or transverse) sections through C. -Xaymacana at successive levels. - -Fig. 17. Tripedalia cystophora, from one of the four interradial sides. - -Fig. 18. The same from below. - -Fig. 19. The same cut in halves vertically through a perradius. - -Fig. 20. The same cut in halves vertically through interradius. - -Figs. 21-30. Diagrams of horizontal sections through T. cystophora at -successive levels. - -(The following are of Charybdea, except when specially stated otherwise.) - -Fig. 31. Horizontal section through the suspensorium. - -Fig. 32. Diagram of a gastric ostium seen from the stomach side. - -Fig. 33. Diagram of a vertical section through a gastric ostium. - -Fig. 34. Diagram of a horizontal section through a gastric ostium. - -Fig. 35. Diagram to illustrate the formation of the central and -peripheral gastro-vascular systems of a Hydromedusa (_a_, _b_, and _c_) -and a Cubomedusa (_d_). - -Fig. 36. Vertical section through the upper part of the bell, adradial, -to show horizontal vascular lamella. - -Fig. 37. Vertical section through the perradius, to show vascular lamella -of the niche of the margin. - -Fig. 38. Vertical section a little to one side of the last, to show same -structure. - -Fig. 39. Horizontal section through the upper part of the sensory niche, -to show vascular lamella of the niche. - -Figs. 40-43. Horizontal sections through the base of a pedalium at -successive levels, _w-x-y-z_, Fig. 5, to show marginal lamella. - -Fig. 44. Diagram to show relations of sensory niche, of bell margin and -velarium in adult Tripedalia. The velarium represented as pendant. - -Fig. 45. To show the same structure in a young Tripedalia. - -Fig. 46. Horizontal section through the last just at the margin, to -compare with Fig. 29. - -Fig. 47. Cross-section through the nerve ring. - -Fig. 48. The structure of the nerve as seen by focusing at successive -levels. - -Fig. 49. Diagram to show the relation of the nerve ring to the sensory -club. - -Fig. 50. Horizontal section through the upper part of the sensory niche, -to show passage of nerve root through gelatine of subumbrella to stalk of -sensory club. - -Fig. 51. Vertical section through base of stalk of sensory club, to show -same passage. - -Fig. 52. Similar section to last, but nearer to perradius, to show -sub-endodermal tract of nerve fibres. - -Fig. 53. Sensory organ in proboscis of Tripedalia, as seen from surface -in living animal. - -Figs. 54 and 55. Sections of same sensory organ. - -Fig. 56. Vertical section through one side of proboscis, to show sensory -organ attached to endoderm. (Tripedalia.) - -Fig. 57. Diagram of the outlines of sensory club seen from the side, by -camera lucida. - -Fig. 58. Part of retina of larger complex eye cut radially. - -Figs. 59-62. Four sections in direct sequence through retinal cells -transversely, larger eye. - -Fig. 63. Transverse section through the tips of cells of a slightly -pigmented retina, larger eye. - -Figs. 64-66. Three transverse sections through vitreous body at different -levels. All from same series, but not in direct sequence; larger eye. - -Fig. 67. Radial section through retina, to show fibres from the long -pigment cells; larger eye. - -Fig. 68. Transverse section through vitreous body of Tripedalia near -retina. - -Fig. 69. Vertical section through smaller complex eye. - -Fig. 70. Wandering cells, Charybdea. - -Fig. 71. Floating mass, from stomach pocket of Tripedalia. - -Fig. 72. Horizontal section through larger complex eye. (See text figure, -p. 50.) - -[Illustration: CUBOMEDUSÆ. PLATE I. - -Gilman Drew, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE II. - -Conant & Crew, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE III. - -F.S. Conant, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE IV. - -F.S. Conant, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE V. - -F.S. Conant, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE VI. - -F.S. Conant, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE VII. - -F.S. Conant, del. Heliotype Co., Boston.] - -[Illustration: CUBOMEDUSÆ. PLATE VIII. - -F.S. Conant, del. Heliotype Co., Boston.] - - - - - -End of the Project Gutenberg EBook of The Cubomedusæ, by Franklin Story Conant - -*** END OF THIS PROJECT GUTENBERG EBOOK THE CUBOMEDUSÆ *** - -***** This file should be named 54241-0.txt or 54241-0.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/4/2/4/54241/ - -Produced by Donald Cummings, Bryan Ness and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - -Updated editions will replace the previous one--the old editions -will be renamed. - -Creating the works from public domain print editions means that no -one owns a United States copyright in these works, so the Foundation -(and you!) can copy and distribute it in the United States without -permission and without paying copyright royalties. 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You may copy it, give it away or -re-use it under the terms of the Project Gutenberg License included -with this eBook or online at www.gutenberg.org/license - - -Title: The Cubomedusæ - -Author: Franklin Story Conant - -Release Date: February 26, 2017 [EBook #54241] - -Language: English - -Character set encoding: UTF-8 - -*** START OF THIS PROJECT GUTENBERG EBOOK THE CUBOMEDUSÆ *** - - - - -Produced by Donald Cummings, Bryan Ness and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - - - - - -</pre> - - -<p class="transnote">Transcriber’s Note: The images contained within black borders -are clickable for a larger version, if you are using a browser/device that supports -this functionality.</p> - -<p><span class="pagenum"><a name="Page_i" id="Page_i">[i]</a></span></p> - -<p class="titlepage">Memoirs from the Biological Laboratory<br /> -<span class="smaller">OF THE</span><br /> -JOHNS HOPKINS UNIVERSITY<br /> -<span class="smaller">IV, 1</span><br /> -WILLIAM K. BROOKS, EDITOR</p> - -<h1>THE CUBOMEDUSÆ</h1> - -<p class="titlepage">A DISSERTATION PRESENTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY,<br /> -IN THE JOHNS HOPKINS UNIVERSITY, 1897</p> - -<p class="titlepage">BY<br /> -<span class="larger">FRANKLIN STORY CONANT</span></p> - -<p class="titlepage">A MEMORIAL VOLUME</p> - -<p class="titlepage">BALTIMORE<br /> -<span class="smcap">The Johns Hopkins Press</span><br /> -1898</p> - -<p><span class="pagenum"><a name="Page_ii" id="Page_ii">[ii]</a></span></p> - -<p class="titlepage smaller">PRINTED BY<br /> -<span class="larger">The Lord Baltimore Press</span><br /> -THE FRIEDENWALD COMPANY<br /> -BALTIMORE, MD., U. S. A.</p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_iii" id="Page_iii">[iii]</a></span></p> - -<div class="figcenter" style="width: 300px;"> - -<img src="images/frontispiece.jpg" width="300" height="531" alt="A photograph of Franklin -Story Conant. Handwritten, beneath: “With the kind regards of Franklin Story Conant.”" /> - -<p class="caption">With the kind regards of Franklin Story Conant.</p> - -<p class="caption">THE HELIOTYPE PRINTING CO. BOSTON</p> - -</div> - -<p><span class="pagenum"><a name="Page_iv" id="Page_iv">[iv]</a></span></p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_v" id="Page_v">[v]</a></span></p> - -<h2>FRANKLIN STORY CONANT<br /> -<span class="smaller">SEPTEMBER 21, 1870—SEPTEMBER 13, 1897</span><br /> -A BIOGRAPHICAL SKETCH</h2> - -<p><span class="pagenum"><a name="Page_vi" id="Page_vi">[vi]</a><br /> -<a name="Page_vii" id="Page_vii">[vii]</a></span></p> - -<p>This Treatise is printed after the author’s death, as a Memorial by -his friends, fellow-students and instructors, with the aid of the Johns -Hopkins University. It consists of his Dissertation, reprinted from the -copy which was accepted by this University at his examination for the -degree of Doctor of Philosophy in June, 1897.</p> - -<p>As he had made many notes on the embryology of the Cubomedusæ, -and had hoped to complete and publish them together with an account -of physiological experiments with these medusæ, he had described the -Dissertation on the title-page as Part I, Systematic and Anatomical, and -he went to Jamaica immediately after his examination to continue his -studies and to procure new material, and he there lost his life.</p> - -<p><span class="pagenum"><a name="Page_viii" id="Page_viii">[viii]</a></span></p> - -<hr class="tb" /> - -<p><span class="pagenum"><a name="Page_ix" id="Page_ix">[ix]</a></span></p> - -<p>Franklin Story Conant was born in Boston on September 21, 1870, -and he died in Boston on September 13, 1897, a few days after his arrival -from Jamaica, where he had contracted yellow fever through -self-sacrificing devotion to others.</p> - -<p>He was educated in the public schools of New England; at the -University of South Carolina; at Williams College, where he received -the degree of Bachelor of Arts in 1893; and in the Johns Hopkins -University, where he received the degree of Doctor of Philosophy in 1897, -and where he was appointed a Fellow in 1896 and Adam T. Bruce Fellow -in 1897.</p> - -<p>Most of his instructors have told us that they quickly discovered that -Conant was a young man of unusual intelligence and energy and uprightness, -and as his education progressed he secured the esteem and the -affectionate interest of all who had him in charge, so that they continued -to watch his career with increasing pride and satisfaction.</p> - -<p>He entered the Johns Hopkins University in the spring of 1894, and -at once joined the party of students in zoology who were working, under -my direction, in the marine laboratory of the University at Beaufort, -North Carolina; and from that time until his death he devoted himself -continually, without interruption, to his chosen subject—spending his -winters in the laboratory in Baltimore, and devoting his summers to out-of-door -studies at Beaufort and at Wood’s Holl, and in Jamaica.</p> - -<p>It is as a student and not as an investigator that we most remember -Conant, for most of his time was given to reading and study on subjects -of general educational value; although he had begun, before his death, -to make original contributions to science and to demonstrate his ability -to think and work on independent lines.</p> - -<p>His study of the Chaetognaths was undertaken only for the purpose -of verifying the account of their anatomy and development in the text -books, but it soon showed the presence at Beaufort of several undescribed -species. Without interrupting his more general studies, he employed -his odd moments for three years in their systematic analysis, and at -last published two papers, “Description of Two New Chaetognaths,” and -“Notes on the Chaetognaths,” which show notable power of close and<span class="pagenum"><a name="Page_x" id="Page_x">[x]</a></span> -accurate observation and of exact description; and, while short, are -valuable contributions to our knowledge of this widely distributed but -difficult group.</p> - -<p>As he appreciated the value to one who has devoted himself to zoology -of thorough acquaintance with physiological problems and the means for -solving them, he wished, after he had completed his general course in -physiology, to attempt original research in this field; and, at the suggestion -of Professor Howell, he, in company with H. L. Clark, his fellow -student, undertook and successfully completed an investigation of which -Professor Howell gives the following account:</p> - -<div class="blockquote"> - -<p>In connection with Mr. H. L. Clark, Mr. Conant undertook to investigate the -character of the nervous control of the heart beat in decapod crustaceans. They -selected the common edible crab, Callinectes hastatus, and made a series of most -careful experiments and dissections which resulted in proving the existence of one -inhibitory nerve and two accelerator nerves passing to the heart on each side from -the thoracic ganglion. They not only demonstrated the physiological reaction of -these nerves, but traced out successfully their anatomical course from the ganglion to -the pericardial plexus. It seemed hardly probable from an a priori standpoint that in -an animal like the crab there should be any necessity for an elaborate nervous mechanism -to regulate the beat of the heart, but their experiments placed the matter -beyond any doubt, and have since served to call attention to this animal as a promising -organism for the study of some of the fundamental problems in the physiology of -the heart. As compared with previous work upon the same subject it may be said -that their experiments are the most definite and successful that have yet been made.</p> - -</div> - -<p>His chief completed work, the Dissertation on The Cubomedusæ, is -here printed; and through it the reader who did not know Conant must -decide whether he was well fitted, by training and by natural endowments, -for advancing knowledge. I myself felt confident that the career -on which he had entered would be full of usefulness and honor. I was -delighted when he was appointed to the Adam T. Bruce Fellowship, for -I had discovered that he was rapidly becoming an inspiring influence -among his fellow students in the laboratory, and I had hoped that we -might have him among us for many years, and that we might enjoy and -profit by the riper fruits of his more mature labors.</p> - -<p>Immediately after his examination for the degree of Doctor of -Philosophy in June, 1897, he set out for Jamaica to continue his -studies at the laboratory which this University had established for the -summer at Port Antonio, and he there worked for nearly three months -on the development, and on the physiology of the sense-organs, of the -Cubomedusæ.</p> - -<p>His notes and specimens are so complete that I hope it will be -possible to complete in Baltimore, at an early day, the work which he -had expected to carry on this year.</p> - -<p><span class="pagenum"><a name="Page_xi" id="Page_xi">[xi]</a></span></p> - -<p>After the sudden and alarming death of the director of the expedition, -Dr. J. E. Humphrey, Conant took the burden of responsibility upon -himself, and while he fully appreciated his own great danger, he devoted -himself calmly and methodically to the service of others who, in their -afflictions, needed his help, and he fell in the path of duty, where he had -always walked, leaving behind him a clear and simple account of all the -business of the laboratory and of his scientific work, and of his own -affairs, complete to the day before his death.</p> - -<p>Immediately after the opening of the University in October his -friends and companions and instructors assembled to express the sorrow -with which they had heard the sad news of his death, and to record their -love and esteem for the generous, warm-hearted friend who in all the -relations of life had proved himself so worthy of their affectionate -remembrance. At this meeting those who had worked at his side in our -laboratories recalled his steadfast earnestness in the pursuit of knowledge, -and the encouragement they had found in his bright example; -while those who had been his instructors spoke of him as one who had -bettered their instruction and enriched all that he undertook by sound -and valuable observations and reflections. While all united in mourning -the untimely loss of one who had shown such rich promise of a life full -of usefulness and honor and distinction, it was pointed out with pride -that his end was worthy of one who had devoted it to the fearless pursuit -of truth, and to generous self-sacrifice and noble devotion to others; and -it was resolved, “That we prize the lesson of the noble life and death of -Franklin Story Conant.”</p> - -<p><span class="pagenum"><a name="Page_xii" id="Page_xii">[xii]</a></span></p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_xiii" id="Page_xiii">[xiii]</a></span></p> - -<h2>LIST OF THE PUBLISHED BIOLOGICAL PAPERS OF FRANKLIN -STORY CONANT.</h2> - -<p>1. <span class="smcap">Description of Two New Chaetognaths.</span> Johns Hopkins University -Circulars, No. 119, June, 1895.</p> - -<p>2. <span class="smcap">Notes on the Chaetognaths.</span> Johns Hopkins University Circulars, -No. 126, June, 1896.</p> - -<p>3. <span class="smcap">The Inhibitory and Accelerator Nerves to the Crab’s Heart</span> -(<i>an abstract</i>), by F. S. Conant and H. L. Clark. Johns Hopkins University -Circulars, No. 126, June, 1896.</p> - -<p>4. <span class="smcap">On the Accelerator and Inhibitory Nerves to the Crab’s -Heart</span>, by F. S. Conant and H. L. Clark. The Journal of Experimental -Medicine, Vol. I, No. 2, 1896.</p> - -<p>5. <span class="smcap">Notes on the Cubomedusæ</span> (<i>an abstract</i>). Johns Hopkins -University Circulars, No. 132, November, 1897.</p> - -<p>6. <span class="smcap">The Cubomedusæ.</span> (This was accepted in June, 1897, as his thesis -for the degree of Doctor of Philosophy, and it is here printed.)</p> - -<p><span class="pagenum"><a name="Page_xiv" id="Page_xiv">[xiv]</a></span></p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_xv" id="Page_xv">[xv]</a></span></p> - -<h2>TABLE OF CONTENTS.</h2> - -<table summary="Contents"> - <tr> - <td></td> - <td class="tdr smaller">PAGE</td> - </tr> - <tr> - <td>INTRODUCTION</td> - <td class="tdr"><a href="#Page_1">1</a></td> - </tr> - <tr> - <td><a href="#Part_I">PART I</a>: SYSTEMATIC</td> - <td class="tdr"><a href="#Page_3">3</a></td> - </tr> - <tr> - <td class="level2">Family I: <span class="smcap">Charybdeidæ</span></td> - <td class="tdr"><a href="#Page_3">3</a></td> - </tr> - <tr> - <td class="level5"><i>Charybdea Xaymacana</i></td> - <td class="tdr"><a href="#Page_4">4</a></td> - </tr> - <tr> - <td class="level2"><span class="ditto">“</span> II: <span class="smcap">Chirodropidæ</span></td> - <td class="tdr"><a href="#Page_4">4</a></td> - </tr> - <tr> - <td class="level2"><span class="ditto">“</span> III: <span class="smcap">Tripedalidæ</span></td> - <td class="tdr"><a href="#Page_5">5</a></td> - </tr> - <tr> - <td class="level5"><i>Tripedalia cystophora</i></td> - <td class="tdr"><a href="#Page_5">5</a></td> - </tr> - <tr> - <td><a href="#Part_II">PART II</a>: GENERAL DESCRIPTION OF THE ANATOMY OF THE CUBOMEDUSÆ</td> - <td class="tdr"><a href="#Page_7">7</a></td> - </tr> - <tr> - <td class="level2">A. <span class="smcap">Charybdea Xaymacana</span></td> - <td class="tdr"><a href="#Page_7">7</a></td> - </tr> - <tr> - <td class="level3">a. Environment and Habit of Life</td> - <td class="tdr"><a href="#Page_7">7</a></td> - </tr> - <tr> - <td class="level3">b. External Anatomy</td> - <td class="tdr"><a href="#Page_8">8</a></td> - </tr> - <tr> - <td class="level4">2. Form of Bell</td> - <td class="tdr"><a href="#Page_8">8</a></td> - </tr> - <tr> - <td class="level4">3. Pedalia</td> - <td class="tdr"><a href="#Page_8">8</a></td> - </tr> - <tr> - <td class="level4">4. Sensory Clubs</td> - <td class="tdr"><a href="#Page_9">9</a></td> - </tr> - <tr> - <td class="level4">5. The Bell Cavity and its Structures</td> - <td class="tdr"><a href="#Page_10">10</a></td> - </tr> - <tr> - <td class="level5">(a) Proboscis</td> - <td class="tdr"><a href="#Page_11">11</a></td> - </tr> - <tr> - <td class="level5">(b) Suspensoria, or Mesogonia</td> - <td class="tdr"><a href="#Page_11">11</a></td> - </tr> - <tr> - <td class="level5">(c) Interradial funnels, or funnel cavities</td> - <td class="tdr"><a href="#Page_11">11</a></td> - </tr> - <tr> - <td class="level5">(d) Velarium</td> - <td class="tdr"><a href="#Page_12">12</a></td> - </tr> - <tr> - <td class="level5">(e) Frenula</td> - <td class="tdr"><a href="#Page_12">12</a></td> - </tr> - <tr> - <td class="level5">(f) Musculature</td> - <td class="tdr"><a href="#Page_12">12</a></td> - </tr> - <tr> - <td class="level5">(g) Nerve ring</td> - <td class="tdr"><a href="#Page_13">13</a></td> - </tr> - <tr> - <td class="level3">c. Internal Anatomy</td> - <td class="tdr"><a href="#Page_13">13</a></td> - </tr> - <tr> - <td class="level4">6. Stomach</td> - <td class="tdr"><a href="#Page_13">13</a></td> - </tr> - <tr> - <td class="level4">7. Phacelli</td> - <td class="tdr"><a href="#Page_14">14</a></td> - </tr> - <tr> - <td class="level4">8. Peripheral Part of the Gastro-Vascular System</td> - <td class="tdr"><a href="#Page_14">14</a></td> - </tr> - <tr> - <td class="level5">(a) Stomach Pockets (Valves and Mesogonial Pockets)</td> - <td class="tdr"><a href="#Page_14">14</a></td> - </tr> - <tr> - <td class="level5">(b) Marginal Pockets</td> - <td class="tdr"><a href="#Page_17">17</a></td> - </tr> - <tr> - <td class="level5">(c) Canals of the Sensory Clubs and Tentacles</td> - <td class="tdr"><a href="#Page_17">17</a></td> - </tr> - <tr> - <td class="level4">9. Reproductive Organs</td> - <td class="tdr"><a href="#Page_19">19</a></td> - </tr> - <tr> - <td class="level4"><span class="pagenum"><a name="Page_xvi" id="Page_xvi">[xvi]</a></span>10. Floating and Wandering Cells</td> - <td class="tdr"><a href="#Page_20">20</a></td> - </tr> - <tr> - <td class="level2">B. <span class="smcap">Tripedalia Cystophora</span></td> - <td class="tdr"><a href="#Page_22">22</a></td> - </tr> - <tr> - <td class="level3">a. Habitat</td> - <td class="tdr"><a href="#Page_22">22</a></td> - </tr> - <tr> - <td class="level3">b. External Anatomy</td> - <td class="tdr"><a href="#Page_23">23</a></td> - </tr> - <tr> - <td class="level3">c. Internal Anatomy</td> - <td class="tdr"><a href="#Page_24">24</a></td> - </tr> - <tr> - <td><a href="#Part_III">PART III</a>: DESCRIPTION OF SPECIAL PARTS OF THE ANATOMY</td> - <td class="tdr"><a href="#Page_27">27</a></td> - </tr> - <tr> - <td class="level2">A. <span class="smcap">Vascular Lamellæ</span></td> - <td class="tdr"><a href="#Page_27">27</a></td> - </tr> - <tr> - <td class="level2">B. <span class="smcap">Nervous System</span></td> - <td class="tdr"><a href="#Page_37">37</a></td> - </tr> - <tr> - <td>LITERATURE</td> - <td class="tdr"><a href="#Page_57">57</a></td> - </tr> - <tr> - <td>TABLE OF REFERENCE LETTERS</td> - <td class="tdr"><a href="#Page_58">58</a></td> - </tr> - <tr> - <td>DESCRIPTION OF FIGURES</td> - <td class="tdr"><a href="#Page_60">60</a></td> - </tr> -</table> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_1" id="Page_1">[1]</a></span></p> - -<h2>INTRODUCTION.</h2> - -<p>Jelly-fish offer to the lover of natural history an inexhaustible store -of beauty and attractiveness. One who has studied them finds within -him a ready echo to Haeckel’s statement that when first he visited the -seacoast and was introduced to the enchanted world of marine life, none -of the forms that he then saw alive for the first time exercised so powerful -an attraction upon him as the Medusæ. The writer counts it a rare -stroke of fortune that he was led to the study of a portion of the group -by the discovery of two new species of Cubomedusæ in Kingston Harbor, -Jamaica, W. I., while he was with the Johns Hopkins Marine Laboratory -in June of 1896.</p> - -<p>The Cubomedusæ are of more than passing interest among jelly-fish, -both because of their comparative rarity and because of the high degree -of development attained by their nervous system. One fact alone suffices -to attract at once the attention of the student of comparative morphology—that -here among the lowly-organized Cœlenterates we find an animal -with eyes composed of a cellular lens contained in a pigmented retinal -cup, in its essentials analogous to the vertebrate structure. Perhaps this -and other facts about the Cubomedusæ would be more generally known, -had they not been to a certain extent hidden away in Claus’s paper on -Charybdea marsupialis (’78), which, while a record of careful and accurate -work, is in many respects written and illustrated so obscurely that -it is very doubtful whether one could arrive at a clear understanding of -its meaning who was not pretty well acquainted with Charybdea beforehand.</p> - -<p>Before Claus’s paper was received at this laboratory, H. V. Wilson -went over essentially the same ground upon a species of Chiropsalmus -taken at Beaufort, N. C. When the article on Charybdea marsupialis -appeared, however, the results were so similar that Wilson did not complete -for publication the careful notes and drawings he had made.</p> - -<p>Haeckel’s treatment of the Cubomedusæ in his “System” (’79) in the -Challenger Report (’81) is much more lucid than Claus’s; but the extended -scope of his work and the imperfect preservation of his material prevented -a detailed investigation, and for a more complete and readily intelligible<span class="pagenum"><a name="Page_2" id="Page_2">[2]</a></span> -account of the structure of the Cubomedusæ a larger number of figures -is desirable.</p> - -<p>In the foregoing facts lies whatever excuse is necessary for repeating -in the present paper much that has already seen print in one form or -another.</p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_3" id="Page_3">[3]</a></span></p> - -<h2 id="Part_I"><span class="smcap">Part I: SYSTEMATIC.</span></h2> - -<p>It seems advisable first of all to establish the systematic position of -the two newly found species, Charybdea Xaymacana and Tripedalia -cystophora. Haeckel’s classification, as given in his “System der -Medusen,” is an excellent one and will be followed in this case. One -of the new species, however, will not classify under either of Haeckel’s -two families, so that for it a new family has been formed and named the -Tripedalidæ. In showing the systematic position of the two new forms, -an outline of Haeckel’s classification will be given, so far as it concerns -our species, together with the additions that have been made necessary.</p> - -<h3><span class="smcap">Cubomedusæ</span> (Haeckel, 1877).</h3> - -<p>Characteristics: Acraspeda with four perradial sensory clubs which -contain an auditory club with endodermal otolith sac and one or several -eyes. Four interradial tentacles or groups of tentacles. Stomach with -four wide perradial rectangular pockets, which are separated by four -long and narrow interradial septa, or cathammal plates. Gonads in four -pairs, leaf-shaped, attached along one edge to the four interradial septa. -They belong to the subumbrella, and are developed from the endoderm -of the stomach pockets, so that they project freely into the spaces of the -pockets.</p> - -<h4>Family I: <span class="smcap">Charybdea</span> (Gegenbaur, 1856).</h4> - -<p>Cubomedusæ with four simple interradial tentacles; without marginal -lobes in the velarium, but with eight marginal pockets; without -pocket arms in the four stomach pockets.</p> - -<h5>Genus: <i>Charybdea.</i></h5> - -<p>Charybdeidæ with four simple interradial tentacles with pedalia; -with velarium suspended, with velar canals and four perradial frenula. -Stomach flat and low, without broad suspensoria. Four horizontal -groups of gastric filaments, simple or double, tuft or brush-shaped, -limited to the interradial corners of the stomach.</p> - -<p><span class="pagenum"><a name="Page_4" id="Page_4">[4]</a></span></p> - -<h6>Species: <i>Charybdea Xaymacana</i> (<a href="#plate1">Fig. 1</a>).</h6> - -<p>Bell a four-sided pyramid with the corners more rounded than -angular, yet not so rounded as to make the umbrella bell-shaped. The -sides of the pyramid parallel in the lower two-thirds of the bell, in the -upper third curving inward to form the truncation; near the top a slight -horizontal constriction. Stomach flat and shallow. Proboscis with four -oral lobes, hanging down in bell cavity a distance of between one-third -and one-half the height of bell; very sensitive and contractile, so that it -can be inverted into the stomach. The four phacelli epaulette-shaped, -springing from a single stalk. Distance of the sensory clubs from the -bell margin one-seventh or one-eighth the height of bell. Velarium in -breadth about one-seventh the diameter of the bell at its margin. Four -velar canals in each quadrant; each canal forked at the ends, at times -with more than two branches. Pedalia flat, scalpel-shaped, between one-third -and one-half as long as the height of bell. The four tentacles, when -extended, at least eight times longer than the bell. Sexes separate. -Height of bell, 18-23 mm.; breadth, about 15 mm. (individuals with -mature reproductive elements); without pigment. Found at Port Henderson, -Kingston Harbor, Jamaica.</p> - -<p>As may be seen from the above, C. Xaymacana differs only a little -from the C. marsupialis of the Mediterranean. Claus mentions in the -latter a more or less well defined asymmetry of the bell, which he -connects with a supposed occasional attachment by the proboscis to algæ. -In C. Xaymacana I never noticed but that the bell was perfectly symmetrical. -C. Xaymacana is about two-thirds the size given by Claus for -his examples of C. marsupialis, which were not then sexually mature. -It has 16 velar canals instead of 24 (32), as given by Haeckel, or 24 as -figured by Claus. Difference in size and in number of velar canals are -essentially the characteristics upon which Haeckel founded his Challenger -species, C. Murrayana.</p> - -<h4>Family II: <span class="smcap">Chirodropidæ</span> (Haeckel, 1877).</h4> - -<p>Cubomedusæ with four interradial groups of tentacles; with sixteen -marginal pockets in the marginal lobes of the velarium, and with eight -pocket arms, belonging to the exumbrella, in the four stomach pockets.</p> - -<p>This family is represented in American waters by a species of -Chiropsalmus, identified by H. V. Wilson as C. quadrumanus, found at -Beaufort, North Carolina.</p> - -<p><span class="pagenum"><a name="Page_5" id="Page_5">[5]</a></span></p> - -<h4>Family III: <span class="smcap">Tripedalidæ</span> (1897).</h4> - -<p>Cubomedusæ with four interradial groups of tentacles, each group -having three tentacles carried by three distinct pedalia; without marginal -lobes in the velarium; with sixteen marginal pockets; without pocket -arms in the stomach pockets.</p> - -<h5>Genus: <i>Tripedalia</i>.</h5> - -<p>For the present the characteristics of family and genus must necessarily -be for the most part the same. The genus is distinguished by -having twelve tentacles in four interradial groups of three each; velarium -suspended by four perradial frenula; canals in the velarium; stomach -projecting somewhat convexly into the bell cavity, with relatively well-developed -suspensoria; four horizontal groups of gastric filaments, each -group brush-shaped, limited to the interradial corners of the stomach.</p> - -<h6>Species: <i>Tripedalia cystophora</i> (<a href="#plate1">Fig. 17</a>).</h6> - -<p>Shape of bell almost exactly that of a cube with rounded edges; the -roof but little arched. The horizontal constriction commonly seen near -the top of the bell in the Cubomedusæ not present. Proboscis with four -oral lobes; hanging down in the bell cavity generally more than half the -depth of the cavity and at times even to the bell margin. In the gelatine -of the proboscis an irregular number (15-21) of sensory organs resembling -otocysts, from the presence of which comes the specific name. -Phacelli brush-shaped, composed of from seven to thirteen filaments -springing from a single stalk in each quadrant, or rarely from two separate -stalks in one of the quadrants. Distance of the sensory clubs from -the bell margin about one-fifth or one-fourth of the height of bell. -Breadth of velarium about one-sixth the diameter of bell at margin; -with six velar canals in each quadrant; the canals simple, unforked. -Pedalia flattened, shaped like a slender knife blade, about half as long as -the height of the bell. Tentacles at greatest extension observed two and -a half times the length of pedalia. Sexes separate. Height of bell in -largest specimens (reproductive elements mature) eight or nine mm. -Breadth same as height or even greater. Color a light yellowish brown, -due in large part to eggs or embryos in the stomach pockets. The reproductive -organs especially prominent by reason of their similar color. -Found in Kingston Harbor, Jamaica.</p> - -<p>It will be seen from the above that Tripedalia possesses two of the<span class="pagenum"><a name="Page_6" id="Page_6">[6]</a></span> -characteristics of the Charybdeidæ and two of the Chirodropidæ. The -family was named from the prominent feature of the arrangement of -the tentacles, in groups of three with separate pedalia. The small size -of T. cystophora is worthy of note in connection with the fact that of the -twenty species of Cubomedusæ given by Haeckel in his “System” only -two are smaller than 20 mm. in height, and those are the two representatives -of Haeckel’s genus Procharagma, the prototype form of the Cubomedusæ, -without pedalia and without velarium. While Tripedalia has -both pedalia and velarium, it may be perhaps that its small size, taken -in connection with characteristics just about midway between the -Charybdeidæ and the Chirodropidæ, indicate that it is not a recently -acquired form of the Cubomedusæ.</p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_7" id="Page_7">[7]</a></span></p> - -<h2 id="Part_II"><span class="smcap">Part II: GENERAL DESCRIPTION OF THE ANATOMY OF THE -CUBOMEDUSÆ.</span></h2> - -<h3>A: <span class="smcap">Charybdea Xaymacana.</span></h3> - -<h4>a. <i>Environment and habit of life.</i></h4> - -<p>1. The Cubomedusæ are generally believed to be inhabitants of deep -water which come to the surface only occasionally. Both of the Jamaica -species, however, were found at the surface of shallow water near the -shore, and only under these circumstances. Whether these were their -natural conditions, or whether the two forms were driven by some -chance from the deep ocean into the Harbor and there found their -surroundings secondarily congenial, so to speak, can be a matter of -conjecture only. C. Xaymacana was taken regularly a few yards -off-shore from a strip of sandy beach not ten minutes row from the -laboratory at Port Henderson. It was seen only in the morning before -the sea-breeze came in to roughen the water and to turn the region of its -placid feeding-ground into a dangerous lee-shore. Some of the specimens -taken contained in the stomach small fish so disproportionately -large in comparison with the stomach that they lay coiled up, head overlapping -tail. The name Charybdea, then, from the Greek χαρύβδις (a gulf, -rapacious), seems to be no misnomer. It is worth mentioning that the -digestive juices left the nervous system of the fish intact, so that from -the stomach of a Charybdea could be obtained beautiful dissections, or -rather macerations, of the brain, cord, and lateral nerves of a small fish.</p> - -<p>In size C. Xaymacana agrees very well with the average of the -genus. The four single tentacles characteristic of the genus are very -contractile, varying from two or three to six or seven inches in length, -and probably if measurements could be taken while the animal was -swimming freely about, the length would be found to be greater still. -Charybdea is a strong and active swimmer, and presents a very beautiful -appearance in its movements through the water, the quick, vigorous -pulsations contrasting sharply with the sluggish contractions seen in -most Scyphomedusæ. With its tentacles streaming gracefully behind, -an actively swimming Charybdea presents a fanciful resemblance to a<span class="pagenum"><a name="Page_8" id="Page_8">[8]</a></span> -comet or meteor. When an attempt is made to capture one, it will often -escape by going down into deeper water—as indeed do other jelly-fish. -Escape from observation is all the more easy by reason of the entire -absence of pigment excepting for the small amount in the sensory clubs. -The yellowish or brownish color usually stated as common in the Cubomedusæ -is nowhere present in C. Xaymacana.</p> - -<h4>b. <i>External Anatomy.</i></h4> - -<p>2. <i>Form of Bell.</i> C. Xaymacana shows the typical division of the -external surface into four almost vertical perradial areas (<a href="#plate1">Figs. 1-3</a>, <i>p</i>), -separated by four stoutly arched interradial ribs or bands (<a href="#plate1">Figs. 1-3</a>, <i>i</i>). -These ribs thus play the part of corners to the Cubomedusan pyramid. -They are formed by the thickenings of the jelly of the exumbrella, and -serve to give the necessary strength to the four interradial corners, each -of which bears one of the four tentacles at its base. Each rib is further -divided into two longitudinal strips by a vertical furrow lying exactly in -the interradius (<a href="#plate1">Fig. 2</a>, <i>ifr</i>). The surface of the exumbrella is thus marked -by twelve longitudinal furrows, as seen in the same figure (<a href="#plate1">2</a>). Of these, -four are the interradial furrows just mentioned; the other eight are the -adradial (<i>afr</i>) furrows, which set off the four perradial surfaces of the -pyramid from the four interradial ribs or bands of the corners, each of -which is again subdivided, as mentioned above, by the shallower interradial -furrows. Each interradial furrow ends above the base of the corresponding -pedalium, at about the level of the sensory club; each adradial -furrow diverges toward the perradius in the lower third of its course, -and thus with its companion furrow narrows down the perradial surface -of the pyramid in the lower part of the bell to an area of not much -greater width than the niches in which the sensory clubs lie. The projecting -interradial corners are of course correspondingly enlarged in the -lower part of the bell, and in this way the contours of the surface are -changed from those figured in the view of the bell from above (<a href="#plate1">Fig. 2</a>) -to those of <a href="#plate1">Fig. 3</a>, which represents a view of the bell margin from below.</p> - -<p>3. <i>Pedalia.</i> From the base of the interradial corner bands spring -the four pedalia (<a href="#plate1">Fig. 1</a>, <i>pe</i>), gelatinous appendages of the margin having -much the same shape as the blade of a scalpel. These in turn bear on -their distal ends, as direct continuations, the long, contractile, simple -tentacles. The relatively stiff pedalia have the same relation to the -flexible tentacles that a driver’s whip-stock has to the long lash. In the -living animal the pedalia are found attached to the margin at an angle<span class="pagenum"><a name="Page_9" id="Page_9">[9]</a></span> -of about 45° with the longitudinal axis of the bell. In the preserved -specimens they are bent in toward the axis by the contraction of the -strong muscles at their base, in which position they are figured by Claus -for C. marsupialis (’78, Taf. I., Figs. 1 and 2).</p> - -<p>The pedalia are in reality processes belonging to the <i>subumbrella</i>, as -will be shown in the section treating of the vascular lamella. They are -composed chiefly of gelatine covered with thin surface epithelium and -carrying within the gelatine the basal portion of the tentacle canals. -They have received various names at the hands of the writers. Gegenbaur -called them “Randblätter.” Claus gave them the name of “Schirmlappen,” -and incorrectly homologized them with the marginal lobes of -other Acraspeda. Claus’s error was corrected by Haeckel, who termed -them “Pedalia” or “Gallertsockel,” and homologized them with the -pedalia of the Peromedusæ. Besides furnishing a base of support for the -tentacles they may perhaps also serve as steering apparatus, a function -for which their thin blade-like form would be admirably adapted.</p> - -<p>Internal to the base of each pedalium, between it and the velarium, -is found a funnel-shaped depression of the ectodermal surface. This is -shown in <a href="#plate2">Fig. 5</a> (<i>ft</i>) in longitudinal section, and in cross-section in <a href="#plate4">Fig. 16</a>. -In the latter figure the epithelium of the outer wall of the funnel (<i>mt</i>) is -shown much thickened, the result of a stout development of muscle -fibres. These are the muscles that in the preserved specimens cause the -inward contraction of the pedalia referred to above.</p> - -<p>4. <i>Sensory Clubs</i> (marginal bodies, rhopalia). In spite of their position -above the bell margin, the four sensory clubs, representing as they -do transformations of the four perradial tentacles, are properly classed -with the pedalia and interradial tentacles as appendages of the margin. -They lie protected in somewhat heart-shaped excavations or niches in -the perradial areas of the exumbrella. Each sensory niche is partially -roofed over by a covering scale, a hood-like projection from the exumbrella. -Below the covering scale the water has free access to the niche -and to the sensory club within it. The sensory club consists of a -hollow stock directly homologous with tentacle and canal, and a terminal, -knob-like swelling, the sensory portion proper. The latter contains -on its inner surface—the surface turned towards the bell cavity—two -complicated unpaired eyes with lens, retina, and pigment, lying one -above the other in the median line; and at the sides of these, two pairs -of small, simple, pigmented, bilaterally symmetrical eye spots. At the -end of the club, that is, on its lowermost point, lies a sac that contains a<span class="pagenum"><a name="Page_10" id="Page_10">[10]</a></span> -concretion and is usually considered auditory. The canal of the stalk is -directly continuous with the gastro-vascular system. In the swollen -knob of the sensory club it forms an ampulla-like terminal expansion.</p> - -<p>As was pointed out by Claus, the bottom of the sensory niche—by -bottom is meant the vertical wall that separates the space of the niche -from the bell cavity—is formed from the subumbrella only. This -arrangement of parts, apparently impossible for a structure so far -removed from the bell margin as the sensory niche, will be explained -more fully under the special topic of the vascular lamellæ, or cathammal -plates. It is sufficient at this point to refer to <a href="#plate6">Fig. 44</a>, which shows the -shield-shaped area mapped out by a vascular lamella that connects the -endoderm of the stomach pocket with the ectoderm of the bottom of -the niche. By this the exumbrella is completely cut off from any part in -the formation of the bottom of the niche. Cross and vertical sections -through the niche (<a href="#plate4">Figs. 39 and 37</a>) help to a better understanding of -these relations. Since the base of the stalk of the sensory niche lies -within the ring of vascular lamella, the whole organ as well as the -bottom of the niche belongs to the subumbrella, and so in spite of its -position some distance upwards from the bell margin the sensory club is -very properly called a “marginal body” (Randkörper).</p> - -<p>The epithelium of the sensory niche consists entirely of the flattened -ectodermal surface layer common to the whole exumbrella. No differentiation -suggestive of nervous function in addition to that of the sensory -clubs can be discovered, although it would be quite natural to expect to -find something of the sort, as intimated by Claus (’78, p. 27).</p> - -<p>It is worth while to mention again the fact that the eyes are directed -inwardly toward the cavity of the bell. The larger and lower of the two -median eyes looks into the bell cavity horizontally; the smaller upper -eye is turned upward toward the region of the proboscis. This is in the -normal pendant position of the sensory club. The stalk, however, is very -flexible, and a range of other positions of the sense organs is possible, -although nothing was observed to suggest that such positions were -within the control of the animal. The eyes evidently have as their chief -function to receive impressions of what is going on <em>inside</em> the bell, not -outside. Perhaps the strongly biconvex, almost spherical lenses of the -median eyes also point to a focus on near and small objects.</p> - -<p>5. <i>The Bell Cavity and its Structures.</i> In general, the bell cavity -repeats the external form of the bell, being almost cubical. In cross-section -it appears very nearly square with the angles in the interradii as<span class="pagenum"><a name="Page_11" id="Page_11">[11]</a></span> -seen in the series of drawings that figure sections of the whole jelly-fish -at different levels (<a href="#plate3">Figs. 6-16</a>). Above, the bell cavity is roofed over by -the stomach; below, it is open freely to the water, the opening being -narrowed somewhat by the diaphragm-like velarium (<a href="#plate1">Fig. 3</a>, <i>v</i>); the four -flat perradial sides are bounded by the walls of the four broad stomach -pockets, to be described when we come to the internal anatomy.</p> - -<p>(a) <i>The Proboscis.</i> From the stomach there hangs down into the -bell cavity the proboscis or manubrium, which consists of a short funnel-shaped -stalk bearing on its distal end the four mouth lobes or lips. The -latter are somewhat broadly V-shaped processes lying in the perradii -with the convexity directed outwards, and with the concavity on the -inside forming the beginnings of four perradial furrows that are continued -upwards to the stomach. The four furrows are shown in the -stalk of the proboscis in <a href="#plate3">Fig. 11</a>, which represents a section taken a little -above the level of the mouth lobes. The same cross-shaped section of the -stalk shows the four perradial prominences or ridges overlying the -furrows, which are the direct continuations of the four projecting mouth -lobes.</p> - -<p>(b) <i>The Suspensoria or Mesogonia.</i> The stomach (leaving out of -consideration the proboscis) hangs down into the bell cavity as a slightly -sagging saucer-shaped roof (<a href="#plate2">Figs. 4 and 5</a>). In the four perradii it is -attached to the lateral walls of the subumbrella by four slenderly developed -mesentery-like structures, the suspensoria or mesogonia. These are -simple ridges of gelatine, covered of course with the epithelium of the -bell cavity, which serve to keep the stomach in position much in the way -that a shelf is supported by brackets (<a href="#plate2">Fig. 4</a>, <i>su</i>). The suspensorium -accordingly has two parts, curved so as to lie at right angles with each -other: a vertical portion lying along the wall of the subumbrella, and a -horizontal which passes over from the vertical on to the basal wall of -the stomach. In <a href="#plate3">Fig. 10</a> the suspensorium in each quadrant is shown -cut across just below the angle between the two parts, so that the two -appear in the section as projections on the wall of the stomach and on -the wall of the subumbrella.</p> - -<p>(c) <i>The Interradial Funnels or Funnel Cavities.</i> It will be seen at -once that the four suspensoria serve as partitions to divide the upper -portion of the bell cavity, the part that lies between the stomach and the -lateral walls of the subumbrella, into four compartments. These compartments -extend upwards in the four interradii like inverted funnels, -whence their name. In the series of cross-sections they can be traced<span class="pagenum"><a name="Page_12" id="Page_12">[12]</a></span> -upwards with constantly diminishing area from the level of the suspensoria, -<a href="#plate3">Fig. 10</a> (<i>if</i>), to <a href="#plate3">Fig. 6</a>, which is taken very near the top of the bell. -Homologous structures exist in all the Scyphomedusæ, and in some of -the Lucernaridæ they are continued up even into the stalk of the -attached jelly-fish.</p> - -<p>(d) <i>The Velarium.</i> Charybdea, like most of the Cubomedusæ, possesses -a velum-like structure around the opening of the bell cavity -(<a href="#plate1">Fig. 3</a>, <i>v</i>). The velarium is a thin muscular diaphragm, resembling the -true velum in position and essential structures, but differing from the -velum in its origin, and in the possession of diverticula from the gastro-vascular -system, the velar canals. Of these there are in C. Xaymacana -very regularly sixteen, four in each quadrant. Their outline is seen in -<a href="#plate1">Fig. 3</a> to be forked with small irregular accessory processes. As for its -origin, the velarium of the Cubomedusæ is commonly accounted to have -arisen by fusion of marginal lobes, as in the case of the velarium of the -Discomedusæ. Pending decisive ontological evidence, the slight notches -in the four perradii seen in <a href="#plate1">Fig. 3</a> may perhaps be taken as slight indications -of a primitive unfused condition, but the question will be brought -up again when the vascular lamellæ are discussed.</p> - -<p>(e) <i>The Frenula.</i> Just as the stomach is attached to the walls of the -subumbrella in the four perradii by the suspensoria, so in the lower part -of the bell cavity the velarium is attached to the wall of the subumbrella -in the perradii by four structures similar to the suspensoria, the frenula -velarii. The frenula, like the suspensoria, resemble the brackets of a -shelf, with the difference that in the case of the frenula the bracket is -above the shelf, their purpose being evidently to keep the velarium stiff -against the outflow of water produced by the pulsations of the bell. -According to the greater need of strength in this case, we find the frenula -stouter, more buttress-like than the suspensoria. The gelatinous ridge -that gives them the necessary firmness is thickened so as to be triangular -in section, as shown in <a href="#plate4">Fig. 16</a> (<i>frn</i>).</p> - -<p>(f) <i>Musculature.</i> As is general in medusæ, the muscular system, so -far as known, is restricted to the subumbrella. It has a very simple -arrangement, consisting of a continuous sheet of circular (<i>i. e.</i> horizontal) -striated fibres, which is interrupted only in the four perradii by the -radially directed muscle fibres of the suspensoria and the frenula. In -each quadrant, between the muscle of the suspensorium above and that -of the frenulum below, in an area just internal to the sensory niche, -there lies a space free from muscle. This interruption of the muscle<span class="pagenum"><a name="Page_13" id="Page_13">[13]</a></span> -layer is shown in <a href="#plate4">Fig. 39</a>. Under the head of musculature belonging to -the subumbrella must be included also the radial, or longitudinal muscles -at the bases of the pedalia, which were mentioned before (<a href="#plate4">Fig. 16</a>, <i>mt</i>). -The mouth lobes and proboscis also are highly contractile and muscular.</p> - -<p>(g) <i>Nerve Ring.</i> It is in the possession of a clearly defined nerve -ring that the Cubomedusæ differ from all other Scyphomedusæ whose -nervous system has been carefully studied. The nerve ring shows very -plainly on the surface of the subumbrella as a well-defined clear streak. -Its course is zig-zag or festoon-like. In the interradii, at the basis of the -tentacles, it lies not far from the bell margin. In the perradii it rises to -the level of the sensory clubs. This very striking arrangement is understood -at once when it is remembered that the sensory clubs represent the -four perradial primary tentacles, and were originally situated on the -margin. When all the rest of the margin grew down and away from -the four sensory clubs, fusing below them to form the present intact -edge of the bell, the four portions of the nerve ring that lay in the -perradii were left at the level of the sensory clubs, and the originally -straight nerve ring was thus bent into a bow in each quadrant. The -finer structure of the nerve will be treated of in the special part to be -devoted to the nervous system.</p> - -<h4>c. <i>Internal Anatomy.</i></h4> - -<p>6. <i>Stomach.</i> The shape of the stomach is approximately that of a -biconvex lens, as seen in <a href="#plate2">Fig. 4</a>, which represents a Charybdea cut in -halves longitudinally in the perradius. The lumen of the proboscis (the -buccal stomach according to Haeckel’s terminology) communicates -directly by a funnel-shaped enlargement with the stomach proper, or -central stomach of Haeckel. The term basal stomach is carried over by -Haeckel from the Stauromedusæ, where it has considerable significance, -to the Cubomedusæ, and applied to the upper part of the central stomach. -In the stalkless Cubomedusæ, however, it has no significance so far as -actual structure goes, and our knowledge of the development of the -Cubomedusæ is as yet too simple for us to say that the upper part of the -main stomach represents what remains of the basal stomach of an -earlier pedunculated stage.</p> - -<p>The epithelium of the roof of the stomach is not specially differentiated -and apparently has little or no part in digestion. The epithelium of -the floor, on the other hand, is composed chiefly of very high and thickly -crowded columnar cells which are usually described as coarsely granular,<span class="pagenum"><a name="Page_14" id="Page_14">[14]</a></span> -but under high powers appear to be filled with vacuoles surrounded by a -network of cell substance. Thickly interspersed among these columnar -cells are goblet cells filled with mucus. The floor is thrown into -numerous wrinkles by ridges in the supporting gelatine resulting in -increase of digestive surface. The four perradial grooves of the proboscis -are continued in the perradii along the floor of the stomach as four fairly -deep furrows, which lead directly to the gastric ostia and stomach -pockets—structures to be described presently. These furrows are lined -with crowded columnar cells, smaller and denser than the other cells of -the digestive epithelium, containing no granules and but little beside the -relatively large, compact, deeply staining nuclei. The furrows probably -represent special ciliated courses.</p> - -<p>7. <i>Phacelli.</i> Lying in the four interradial corners of the stomach are -the four phacelli or tufts of gastral filaments to the number of thirty or -thirty-five in each tuft. The filaments are attached to a single stalk, like -the fringe of an epaulette or the hairs of a coarse brush. The stalk -bearing the filaments is an outgrowth of the lower wall of the stomach -just at the point where it fuses with the upper. The phacelli are therefore -structures of the subumbrella, proof of which will be found under -the special topic of the vascular lamellæ. The stalk, an indication of -which appears in <i>sph</i>. <a href="#plate3">Fig. 6</a> (the section being a little below the axis of -the stalk, which lies horizontally), consists of a firm core of gelatine -covered with the high columnar epithelium of the floor of the stomach. -The filaments themselves are slender processes repeating the structure of -the stalk and having a central axis of gelatine for support covered with -glandular epithelium, which in the case of the filaments bears numerous -nettle cells. These processes are extremely contractile, and in the living -animal show a continuous, slow, squirming movement like a mass of -worms. The section just referred to (<a href="#plate3">Fig. 6</a>) shows diagrammatically -three of these filaments (<i>fph</i>) cut across in each quadrant.</p> - -<p>8. <i>Peripheral Part of the Gastro-vascular System.</i> The proboscis and -stomach proper comprise the central part of the gastro-vascular system. -In direct communication with the central is a peripheral part composed -of pouches or pockets lying in the vertical sides of the cube-shaped bell, -just as the central stomach lies in its roof. The peripheral part may be -subdivided for convenience of description into the stomach pockets, the -marginal pockets, and the canals of the tentacles and sensory clubs.</p> - -<p>(a) <i>Stomach Pockets.</i> These are four broad, thin pouches lying -between the exumbrella and the subumbrella in the four perradii (<i>e. g.</i><span class="pagenum"><a name="Page_15" id="Page_15">[15]</a></span> -<a href="#plate3">Fig. 9</a>, <i>sp</i>) and separated from one another in the interradii merely by -four thin vertical strips of vascular lamella (<i>ivl</i>) or fusion between the two -endodermal surfaces of a primitively single undivided peripheral cavity. -The structure is exactly that which we should have if in a Hydromedusa, -for example Liriope (Trachomedusæ), the four radial canals broadened -out and the intervening cathammal plates correspondingly narrowed, -until the relations in size were just reversed, and instead of four narrow -radial canals separated from one another by four broad cathammal -plates, we had four broad radial canals or pouches separated by four -narrow cathammal plates.</p> - -<p>The stomach pockets communicate at their top with the central -stomach by means of four moderately large openings, the gastric ostia. -These are seen in a side view of the whole animal as triangular spaces -(<a href="#plate1">Fig. 1</a>, <i>g. o.</i>) near the top of the broad perradial sides. In <a href="#plate3">Figures 7 and -8</a> they are seen in cross-sections, in <a href="#plate2">Fig. 4</a> in vertical section.</p> - -<p>The communication between the stomach and each stomach pocket -is guarded by a valve that can cut the one entirely off from the other. -The valve is simply the flexible lower margin of the gastric ostium, a thin -vertical fold of the floor of the stomach, semilunar in shape, just at the -point where it is passing over into the stomach pocket. A longitudinal -section, such as is shown in <a href="#plate2">Fig. 4</a>, gives the best idea of the form and -position of the valve that can be obtained from any simple section. -Internal to the valve is seen a depression of the stomach wall, almost -worthy to be called a pocket. The valve itself lies as a wall across the -end of this depression, obstructing a free course to the stomach pocket. -It will be seen at once that any pressure of fluids in the stomach against -this vertical wall, or valve, would serve only to press it against the inner -surface of the exumbrella, and thus effectually close the entrance into -the stomach pocket. Such a closure would both keep the juices of the -stomach from entering the pockets and the embryos in the pockets from -entering the stomach before the proper time.</p> - -<p>The depression of the floor of the stomach just internal to the valve -may possibly be a structure of some morphological significance. In one -series of sections it was found that in two of the quadrants the depression -was deeper than that represented in <a href="#plate2">Fig. 4</a>, and extended perceptibly into -the outer or vertical portion of the suspensorium. <a href="#plate7">Fig. 32</a> is a diagram -giving a vertical reconstruction in the perradius of the cross-sections in -which this deepened depression was noticed. <a href="#plate7">Fig. 31</a> is a drawing (the -outline by camera lucida) of one of the cross-sections, through the lowermost<span class="pagenum"><a name="Page_16" id="Page_16">[16]</a></span> -point of the depression. The figure gives the wall of the stomach -lined with high columnar epithelium (<i>ens</i>), and the wall of the stomach -pockets, with the suspensorium (<i>su</i>) connecting them. The section is -taken just above the broad angle that lies between the two parts of the -suspensorium, that is, in a plane parallel to the arrow <i>a-b</i> in <a href="#plate7">Fig. 32</a>, but -a little lower down. At the points to which the reference letter <i>x</i> (<a href="#plate7">Fig. -31</a>) refers are seen the first indications of the division into two parts, <i>i. e.</i> -of the apex of the angle. The next section or two lower down show the -relation seen in <a href="#plate3">Fig. 10</a> (<i>su</i>). There can be no doubt in this case that the -depression or pocket lies in the outer vertical limb of the suspensorium. -It is the position that gives it at least the appearance of some morphological -significance. In two genera of Lucernaridæ named and -described by Clark (’78), Halicyathus and Craterolophus, the mesogonia -or suspensoria in all four perradii contain broad pockets. These mesogonial -pockets in the Lucernaridæ have given rise to considerable misunderstanding -owing to the fact that in some forms the reproductive -organs bulge out from the stomach pockets in which they structurally -lie, and come to take up a secondary position in the walls of the mesogonial -pockets. The sections of Charybdea above referred to indicate that -among the Cubomedusæ we may have the same structure reduced to its -lowest terms, and may be a feather’s weight in favor of the view that the -Cubomedusæ are descendants of an attached Lucernaria-like form.</p> - -<p>Two more diagrams, <a href="#plate7">Figs. 33 and 34</a>, are added in order to give a -more complete understanding of a gastric ostium and its neighboring -structures, the mesogonial pocket and the valve. <a href="#plate7">Fig. 33</a> is a view of the -gastric ostium and valve from the stomach side, and represents the -appearance that would be given by a thick section through the arrow <i>x-y</i> in -<a href="#plate7">Fig. 32</a>, in a plane at right angles to the paper. The heavy lines outlining -the gastric ostium (<i>enr</i> and <i>enfl</i>) represent the place where the plane of the -section has cut across the epithelium of the roof of the stomach above the -ostium and the epithelium of the floor of the pocket-like depression -internal to the valve. The continuation of the two heavy lines in either -side of the ostium represents the region where the roof and floor of the -stomach meet; <i>i. e.</i>, the edge of the lens-shaped stomach. The semilunar -outline of the valve (<i>vg</i>) is shown by a light line just above the epithelium -of the depression. As is seen by the reference arrow in <a href="#plate7">Fig. 32</a>, the valve -lies a little external to the immediate plane of the section, and hence it is -that its inner surface is seen in <a href="#plate7">Fig. 33</a> and not a section of it. The -vertical part of the suspensorium (<i>su</i>) is seen in section below the epithelium<span class="pagenum"><a name="Page_17" id="Page_17">[17]</a></span> -of the depression. The reference numbers 1, 2, 3 and 4 denote the -same points in <a href="#plate7">Figs. 32 and 33</a>. <a href="#plate7">Fig. 32</a> referred to <a href="#plate7">Fig. 33</a> would lie in a -plane at right angles to the paper through the reference arrow <i>x-v</i> of the -latter figure.</p> - -<p><a href="#plate7">Fig. 34</a> represents a horizontal section through the gastric ostium at -the level of the arrow <i>a-b</i> in <a href="#plate7">Fig. 32</a>, or arrow <i>c-d</i> in <a href="#plate7">Fig. 33</a>. The reference -numbers 5, 6 and 7, 8 denote similar points in the two figures <a href="#plate7">33 and 34</a>. -<a href="#plate7">Fig. 32</a> as referred to <a href="#plate7">Fig. 34</a> is through the arrow <i>e-f</i>; <a href="#plate7">Fig. 33</a> is through the -arrow <i>c-d</i>. In the series of cross-sections, <a href="#plate3">Fig. 9</a> is taken at a level a little -below that of <a href="#plate7">Fig. 34</a>, and passes through the basal part of the valve (<i>vg</i>).</p> - -<p>(b) <i>Marginal Pockets.</i> The part of the peripheral portion of the gastro-vascular -system in each quadrant which is called the stomach pocket -extends downwards as far as the sensory niche. Here by the coming -together of the walls of the exumbrella and subumbrella the space between -them is obliterated (<a href="#plate4">Fig. 15</a>) in the immediate perradius. From the -sensory niche downward to the margin each stomach pocket is thus -divided into two smaller pouches, the marginal pockets (<i>mp</i>). In each -side of the Cubomedusan cube there are, then, in Charybdea two -marginal pockets; or in all eight, a characteristic of the family Charybdeidæ. -The marginal pockets as the name implies extend downwards to -the bell margin, and are continued into the velarium as the velar canals. -Of these (<a href="#plate1">Fig. 3</a>) there are two from each marginal pocket, or sixteen in -all. The constancy in their number is one of the characteristics that -distinguish C. Xaymacana from the very closely related C. marsupialis -of the Mediterranean. (Compare <a href="#plate1">Fig. 3</a> with the similar one by Claus -for C. marsupialis, ’78, Taf. I., Fig. 6.) The forked shape, while to be sure -the common form in C. marsupialis, is an almost invariable characteristic -in C. Xaymacana. It may be mentioned again that the presence of -these canals is one of the chief features that distinguish the velarium -of the Scyphomedusæ from the velum of the Hydromedusæ.</p> - -<p>(c) <i>Canals of the Sensory Clubs and Tentacles.</i> The four interradial -definitive tentacles and the four perradial transformed tentacles, the -sensory clubs, are hollow, and their canals communicate directly with -the peripheral part of the gastro-vascular system. The canal of the -sensory club in each quadrant leads directly out from the stomach by a -somewhat funnel-shaped opening formed by the approximation of the -two walls of the stomach pocket. The relation of the canal of the sensory -club to the stomach pocket is seen at a glance in <a href="#plate4">Fig. 37</a>. It is given -by means of cross-sections in <a href="#plate3">Figs. 12-14</a>. <a href="#plate3">Figure 12</a> shows the inner<span class="pagenum"><a name="Page_18" id="Page_18">[18]</a></span> -walls of the stomach pocket approaching the outer at two points, leaving -between them a concavity freely open to the rest of the stomach pocket -above and at the sides. <a href="#plate3">Fig. 13</a>, a little lower down, shows the two walls -fused together at two points, making the interspaces a definite canal -communicating with the stomach pocket above only. This canal lies -directly over the sensory niche, and in the next figure (<a href="#plate4">No. 14</a>) the canal -is seen to have passed through the roof of the sensory niche and to have -entered the base of the stalk of the sensory club. In the enlarged end of -the club, the part which bears the sensory structure, the canal widens -into a terminal ampulla-like sac.</p> - -<p>The endoderm lining the canal of the sensory club is specially differentiated. -In the stalk it is more columnar than the epithelium of the -stomach pockets, and is made up of cells containing a brightly staining -nucleus with very little trace of cytoplasm. The cell bodies appear as if -filled with a clear, non-staining fluid. Perhaps these cells give the stalk -elasticity to act in connection with the thin layer of longitudinal muscle-fibres -that are found just external to the supporting lamella. The epithelium -of the terminal enlargement of the canal is composed of very high -narrow cells, many of which show two nuclei of equal size and staining -quality lying side by side.</p> - -<p>In continuation of the specialized epithelium of the perradial furrows -in the floor of the stomach the inner wall of the stomach pocket -shows a strip of similar densely crowded columnar cells leading from -the gastric ostium downwards to the canal of the sensory club. As in -the other case, the strip probably represents a specially ciliated tract, and -perhaps in it we see the reason why the canal of the sensory club is -almost always found to contain either spermatozoa which are shed by -the male reproductive organs directly into the stomach pocket, or else -floating cells of the kind to be described in the next section.</p> - -<p>The canals of the interradial tentacles arise from the peripheral -gastro-vascular system much lower down than those of the sensory -clubs, since these tentacles have preserved their primary positions with -reference to the bell margin. <a href="#plate4">Figure 16</a> represents a section taken at the -level of the base of the pedalia which gives the connection of the tentacle -canals with the gastro-vascular system. At the level below the sensory -niche the four broad stomach pockets have been divided, as we have seen, -into the right marginal pockets (<i>mp</i>). The figure shows that in the -interradial corners the longitudinal septa (<i>ivl</i>, in the preceding figures), -or lines of fusion between the two walls of the peripheral gastro-vascular<span class="pagenum"><a name="Page_19" id="Page_19">[19]</a></span> -space, which divide the primitively simple space into the four stomach -pockets, have come to an end, leaving a connecting canal (<i>cc</i>) in each -corner as all that remains of the primitive uninterrupted communication -between all parts of the peripheral system. It is from these four -connecting canals that the tentacle canals take their origin. From this -point of origin each tentacle canal passes downwards, surrounded by the -gelatine of the pedalium, into the tentacle proper.</p> - -<p>The connecting canals are of morphological importance in that they -are supposed, with much reason, to represent in the Cubomedusæ the -circular canal of the Hydromedusæ.</p> - -<p>9. <i>Reproductive Organs.</i> The sexes are separate in Charybdea. In -both sexes the reproductive organs consist of four pairs of long leaf-like -bodies, each leaf attached along one edge to the wall of the subumbrella -in an interradius (see <a href="#plate1">Fig. 1</a>, <i>r</i>), and hanging free in the stomach pockets. -From this position in the stomach pockets it is evident that the reproductive -organs are endodermal. The lines of attachment of each pair is -just internal to the longitudinal vascular lamella that fuses the outer -and inner walls of the stomach pockets together in the interradius (<i>ivl</i>), -and the reproductive organs are therefore structures belonging to the -subumbrella. It is interesting to note how careful examination of the -medusan organization takes away from the importance of the outer cup, -the exumbrella, and adds to that of the inner, the subumbrella. We -have seen that the phacelli and the sensory clubs, from whose position it -would be supposed that they belonged to the exumbrella, are organs of -the subumbrella, and that there is no muscle-tissue in the exumbrella; -we find now that the reproductive organs belong to the subumbrella, -and it will be shown later that the tentacles, like the sensory clubs, are -structures of the subumbrella also. To the exumbrella are left only the -functions of support and covering.</p> - -<p>The mature reproductive organs extend very nearly throughout the -entire vertical length of the bell, and are therefore found in the series of -cross-sections in all but the uppermost and lowermost (<a href="#plate3">Figs. 7-15</a> <i>r</i>). -The organs consist of germ cells within, covered by an epithelium of -columnar cells that shows here and there nettle cells. The ova are found -with different amounts of yolk, according to age, surrounding a large -nucleus almost devoid of chromatin and an intensely staining nucleolus. -In young ova there appears very plainly in every case at least one small -deeply staining body inside the nucleus, which very much resembles the -nucleolus. These are probably so-called yolk nuclei, and while I have not<span class="pagenum"><a name="Page_20" id="Page_20">[20]</a></span> -made a special study of the ovogenesis, I infer that the constant presence -of at least one, points to an origin of the ovum from a syncytium (of at -any rate two cells), similar to that which has been recently shown by -Doflein (’96) to occur in the formation of eggs in Tubularia. In the -nearly mature ovary each ovum is surrounded by a layer of gelatine, -which comes from the gelatinous sheet that enters the leaf-like ovary for -its support along its line of attachment just internally to the interradial -septum. It seems as if the ova, arising in the epithelium on the surface, -pushed their way into the gelatine inside and there completed their -development entirely surrounded by a slight investment of gelatine, -which grows thinner around each ovum as it increases in size. In males -the testes always show a similar division into compartments by gelatinous -meshes, the compartments thus mapped out being filled with the -small brightly staining spermatocytes. Ova and spermatozoa when -mature are set free in the stomach pockets.</p> - -<p>10. <i>Floating and Wandering Cells.</i> In the stomach pockets, the -canals of the sensory clubs, and even in the stomach itself, are found in -varying numbers freely floating cells having the appearance of young -ova. They vary in size, the smallest being of the size and having the -general aspect of the small ovocytes found in the ovary. The largest -(<a href="#plate4">Fig. 70</a>) have exactly the same structure as the young ovarian eggs -before they have begun to accumulate yolk. The granular deeply staining -cytoplasm, the clear non-staining nucleus with its bright nucleolus -and the nucleolus-like yolk nucleus, all show beyond doubt that these -freely floating cells originate in the ovary.</p> - -<p>In some of my preparations these cells are found not only floating -free, but wandering through the tissues. <a href="#plate4">Fig. 70</a> shows two such wandering -cells fixed just as they were making their way either through the -digestive epithelium into the gelatine of the floor of the stomach, or from -the gelatine into the epithelium. The former seems the more probable, -though why they should want to get into the gelatine is not very easy to -conceive.</p> - -<p>Perhaps there is some connection between this and the appearance -that the young ovarian eggs have of pushing their way from the epithelium -into the gelatine of the ovary. And of course it is not impossible -that the whole phenomenon is abnormal, due to rupture of the ovaries -which sets free young ova to exhibit their amœboid tendencies under -new conditions. Against such an explanation, on the other hand, might -be urged the fact that what seem to be the small floating cells are found<span class="pagenum"><a name="Page_21" id="Page_21">[21]</a></span> -occasionally in males as well as females, and that in the females a series -can be traced with a good degree of certainty between the small floating -cells like those found in the walls, and the larger ones which have all the -characteristics of young ova.</p> - -<p>However that may be, this amœboid action of cells having the structure -of ova brings to mind the remarkable form of asexual reproduction -described by Metschnikoff for Cunina proboscidea, under the name of -“Sporogonie.” Unfortunately Metschnikoff’s original paper was not -accessible to me, so that I was unable to obtain more particulars on the -subject than those given in Korschelt and Heider’s text-book (p. 33). -The reproductive organs of both males and females of Cunina proboscidea -are said to produce, besides the usual distinctively sexual elements, -neutral amœboid germ cells, which wander into the endoderm of the -stomach and circular canal, and also penetrate into the gelatine of the -subumbrella. These amœboid cells divide parthenogenetically. One of -the two cells of the first cleavage continues to divide and eventually -forms an embryo of Cunina; the other remains amœboid and serves for -movement, attachment and nourishment of the embryo.</p> - -<p>Charybdea, however, has shown no sign of any such reproductive -process on the part of its floating and wandering cells. The only indication -that I get as to their use points to a possible nutritive function. -The enlarged terminal portion of the canal of the sensory club almost -invariably contains a number of the small-sized floating cells. These -have a vacuolated, half disintegrated appearance, with the nucleus always -compact and brightly staining. Now, examination of the high columnar -cells that line the enlargement of the canal shows the presence in the -cells of bodies of exactly the same appearance as those in the lumen. In -one case a floating cell was found just at the end of an epithelial cell, to -all appearance half ingested. The identity of the bodies inside the cells -and those in the lumen is shown very clearly in some sections of material -fixed in formalin, which preserves nuclei, cell walls and general outlines -well enough, but does not retain the cytoplasm, and hence is useless for -most purposes of histology. In the endodermal cells of the terminal -enlargement thus preserved are found all the more distinctly the bright, -compact, degenerated nuclei of the ingested cells, while in the lumen are -seen other bright, compact nuclei with the poorly preserved remains of -cell substances around them. In addition to the evidence from the -appearance of the floating cells themselves and their ingestion by the -endodermal cells, a little collateral evidence may perhaps be brought in<span class="pagenum"><a name="Page_22" id="Page_22">[22]</a></span> -from the Tripedalia about to be described. From the ovaries in this -form are detached masses of cells (<a href="#plate4">Fig. 71</a>) which float free in the -stomach pockets among the developing embryos, and to judge from the -vacuolation that appears, are used up in their favor. These cell masses -are described more fully in the part on Tripedalia.</p> - -<h3>B: <span class="smcap">Tripedalia Cystophora.</span></h3> - -<h4>a. <i>Habitat.</i></h4> - -<p>The species upon which the new family was founded was obtained in -great abundance in one locality in Kingston Harbor in the summer of -1896. The environment was even more unlike that in which Cubomedusæ -have been found heretofore than in the case of Charybdea Xaymacana. -On the west side of the Harbor there is a part more or less cut off -from the main body of water, and so from the ocean, by a peninsula. -This sheltered bay is dotted with small mangrove islands which toward -the head of the bay become so numerous as virtually to convert it into a -mangrove swamp. The water is shallow and discolored with organic -matter, showing that the tide does not exercise much influence here, and -the bottom is for the most part a black mud, deep enough to make -wading very uncomfortable but not impossible near shore. The islands -rise but slightly above the level of the waters, and the thick vegetation -that covers them, for the most part mangroves, grows out into the water -on all sides, forming a fringe of overhanging boughs. It was here in the -shelter of the boughs, among the roots and half-submerged stems of the -mangroves, that the small Cubomedusa was found to thrive. It could -be obtained in great abundance almost any day, and of all sizes from the -largest adults with stomach pockets filled with eggs or embryos down to -small specimens only about two millimeters in diameter. In but one -other place was Tripedalia found, and that was a similar region of half -landlocked water skirted with mangroves, situated near Port Royal, -across the harbor from the locality just mentioned. It would be hard to -find places in which the conditions of life were more strikingly different -from those of the pure deep sea in which the Cubomedusæ have been -generally found before. The slight brownish yellow pigment made the -small medusæ a little difficult to see in the discolored water, but like the -pellucid Charybdea in the clear water of the harbor, their active movements -gave away their presence. The swimming was very vigorous and -was effected by quick, strong pulsations (as many as 120 per minute were -counted), very different from the slow, rhythmic contractions of the<span class="pagenum"><a name="Page_23" id="Page_23">[23]</a></span> -Discomedusan Cassiopea which was found in the same region over by -Port Royal. Whether or not the animal made intentional efforts to -escape capture could not be decided satisfactorily, but certain it was that -they did escape often enough by swimming quickly below the surface of -the semi-opaque water.</p> - -<p>Tripedalia endured captivity much more hardily than the Charybdea, -and would live in aquaria happily enough for a number of days—no -attempt was made to see how long. Specimens with their stomach -pockets filled with ripe spermatozoa, or with young at any stage from -egg to planula, were taken in plenty from the latter part of June to the -latter part of July. In each female the young were all at the same -stage. The embryos were thrown out in the aquaria as free-swimming -planulæ, which settled down on the bottom and sides of the glass in a -day or two, and quickly developed into small hydras with mouth and -typically with four tentacles (and four tænioles, W. K. B.), though three -and five were by no means uncommon. In this condition they lived for -three weeks without essential change, and they were still giving no -promise of further development when the laboratory broke up and the -jars had to be emptied.</p> - -<h4>b. <i>External Anatomy.</i></h4> - -<p>The structure of the Cubomedusæ seems to be that of a type well -established, and accordingly offers no very wide range of diversity among -the different genera. The Charybdea that has just been described is a -very typical form and will serve well as a standard with which to compare -our species of Tripedalia. The resemblances are so close that a -detailed account of the anatomy of the second form would involve much -needless repetition. It is hardly necessary to do more than merely point -out in what points Tripedalia resembles Charybdea and in what points it -differs.</p> - -<p>The form of the bell is less pyramidal than in Charybdea. Some -measurements even gave the breadth greater than the height. The -external surface is divided, as typical for the Cubomedusæ, into the four -perradial sides and the four convex interradial ridges, and the furrows -that separate these areas are with one small exception exactly the same -as those of Charybdea, as may be seen by comparing the series of -sections of Tripedalia (<a href="#plate5">Figs. 21-30</a>) with those of Charybdea (<a href="#plate3">Figs. 6-15</a>). -The exception is almost too slight to mention. The adradial furrow in -each octant which sets off the corner rib from the perradial surface in<span class="pagenum"><a name="Page_24" id="Page_24">[24]</a></span> -the lower part of the bell is not directly continuous, as in Charybdea, with -the corresponding furrow in the upper part of the bell—that is, the <i>afr´</i> -of <a href="#plate5">Figs. 24-27</a> is not continuous with the <i>afr</i> of <a href="#plate5">Figs. 22 and 23</a>, as is seen -by both being shown in <a href="#plate5">Fig. 24</a>. The upper furrow (<i>afr</i>) is continued -only a short distance, however, below the starting point of the lower (<i>afr´</i>).</p> - -<p>The pedalia conform entirely to the description given those of -Charybdea, except that there are three attached to the bell margin in -each interradius instead of one, and that the blade of each pedalium is -much narrower.</p> - -<p>The sensory clubs also show exactly the same relation to the bell and -exactly the same structure.</p> - -<p>In the bell cavity the proboscis has a longer and better defined stalk -than that of Charybdea, and has the further and more important difference -of possessing special sensory organs, to the number of fifteen or -twenty. The suspensoria are much more developed than in Charybdea, -so that the interradial funnels lying between are more marked. In a -corresponding way the frenula are larger and stouter (<a href="#plate6">Figs. 28, 29</a>, <i>frn</i>). -The musculature shows no new features and differs only in being comparatively -more strongly developed and having a more pronounced -striation. The nerve ring follows the same looped course from the -margin in each interradius up to the level of the sensory clubs in the -perradius.</p> - -<h4>c. <i>Internal Anatomy.</i></h4> - -<p>The stomach offers no peculiarities, and the phacelli also agree with -those of Charybdea except in having a smaller number of filaments in -each tuft. The stomach pockets are not guarded by such well-developed -valves as those described for Charybdea, though the valvular nature of -the lips of the gastric ostia is indicated and the valvular functions -undoubtedly performed. The gastric ostia are smaller (cf. Figs. <a href="#plate3">7</a> and -<a href="#plate5">22</a>), and this makes highly developed valves less necessary. No trace of -anything corresponding to mesogonial pockets was noticed.</p> - -<p>In the matter of the marginal pockets, however, we find that the -agreement with Charybdea is no longer continued. The regions that -correspond to the eight marginal pockets of Charybdea are formed, as in -that genus, by the coming together of the exumbrella and subumbrella -at the sensory niche (<a href="#plate5">Figs. 25-28</a>), but each of these regions is subdivided, -as it is not in Charybdea, into two marginal pockets, a larger (<i>mp</i>, <a href="#plate6">Figs. -28-29</a>) and a smaller (<i>mp´</i>). In this way sixteen marginal pockets are<span class="pagenum"><a name="Page_25" id="Page_25">[25]</a></span> -formed as in the Chirodropidæ. Furthermore, as happens in the latter -family but does not in the Charybdeidæ, the marginal pockets extend -into the velarium. From each of the larger marginal pockets are given -off two velar canals, while each of the smaller gives rise to but one short -one (<a href="#plate1">Fig. 18</a>). <a href="#plate6">Fig. 30</a> represents one of the last sections of a Tripedalia -cut transversely, in which nothing but the pedalia and the velarium -appear, and in it are shown the velar canals (<i>vc</i>), which come from the -larger marginal pockets. The velarium appears in four segments because -it is drawn upwards in the four perradii by the frenula (see <a href="#plate2">Fig. 20</a>). -That the canals from the smaller pockets do not appear in the section is -due to their shortness and to the fact that they are pulled upwards above -the level of the sections by the frenula, together with that portion of the -velarium.</p> - -<p>The smaller velar canals, a pair in each perradius, seem to have in -the males some function in connection with the storing of matured spermatozoa. -In specimens with ripe testes they are very often found -crowded to distension with spermatozoa, while the other velar canals -may or may not contain them, and generally do not. The epithelium -lining them is, like that of the others, composed of columnar cells higher -on the wall turned toward the bell cavity than on that turned towards -the exterior, but otherwise not specially differentiated. I searched in -vain for any trace of opening by which the spermatozoa might gain the -exterior. <a href="#plate6">Fig. 29</a> shows another point which may be mentioned in -passing, namely, that the canal of each of the three tentacles opens -into the peripheral gastro-vascular system independently. The central -tentacle of each group is the homologue of the single tentacle of Charybdea, -and is formed in Tripedalia before the two lateral tentacles appear. -Its communication with the peripheral pocket system is higher up than -the openings of the lateral tentacles, so that in the section drawn the -latter are just beginning to be indicated (<i>ct´</i>).</p> - -<p>It remains only to speak of the reproductive organs of Tripedalia. -The sexes are separate in this form also, and ovaries and testes have the -same structure as is found in other Cubomedusæ. The development of -floating masses of cells in the females, however, is a feature which, so far -as I know, has not been observed before. These masses, of which a -small one is represented in section by <a href="#plate4">Fig. 71</a>, are apparently developed -along with the eggs, and repeat the structure of the ovary to all intents -the same as if they were various-sized fragments of it broken loose. -They consist mostly of high, columnar epithelial cells surrounding a few<span class="pagenum"><a name="Page_26" id="Page_26">[26]</a></span> -central cells and showing here and there a nettle cell just as the reproductive -organ does. The epithelial cells differ from those of the ovary in -containing one or more large vacuoles, and this vacuolation increases as -the embryos, among which the masses float, develop. The idea naturally -suggests itself, therefore, that they serve for nourishing and perhaps for -protecting the embryos while they are developing in the stomach pockets -of the mother individual.</p> - -<hr class="chap" /> - -<p><span class="pagenum"><a name="Page_27" id="Page_27">[27]</a></span></p> - -<h2 id="Part_III"><span class="smcap">Part III: DESCRIPTION OF SPECIAL PARTS OF THE -ANATOMY.</span></h2> - -<h3>A: <span class="smcap">The Vascular Lamellæ.</span></h3> - -<p>In Medusæ it is a common thing to find that in certain definite -places of the gastro-vascular system two endodermal surfaces that were -primarily separated by a space have come together and fused into a -single lamella or plate. Such a structure is called indifferently a -cathammal plate, an endodermal lamella, or a vascular lamella. In the -adult animal the vascular lamellæ are by virtue of their very nature -formations “with a past.” They are scaffolding left in the completed -structure, giving us clues as to the way in which that structure was -brought about; and in the Cubomedusæ, whose development is as yet -unknown, they therefore afford an unusually interesting subject for -special consideration.</p> - -<p>The vascular lamellæ that are found in Charybdea and Tripedalia -may for convenience be described as forming two systems, the internal -and the marginal. The former comprises the endodermal fusions that -separate the stomach from the stomach pockets (except for the spaces of -communication left free, the gastric ostia) and those that separate the -stomach pockets from one another. The marginal system consists of -the lamella that connects <em>endoderm</em> of the gastro-vascular system with -<em>ectoderm</em> of the surface in a ring all around the bell margin, and with it -also the vascular lamella of the sensory niche, which has already been -referred to in the general description of Charybdea. The lamellæ of the -internal system have been described by previous writers, and especially -by Claus in his paper on Charybdea, but they are still in need of comprehensive -and clear treatment. The lamellæ of the margin and of the -sensory niche have also been described by Claus, but not thoroughly or -with entire accuracy, nor did he recognize the vascular lamellæ of the -sensory niche as originally a part of the lamellæ of the margin. This last -was first determined by H. V. Wilson upon specimens of Chiropsalmus -quadrumanus obtained at Beaufort, North Carolina. Professor Wilson’s -unpublished notes on Chiropsalmus were very kindly placed in my<span class="pagenum"><a name="Page_28" id="Page_28">[28]</a></span> -hands, and so far as the vascular lamellæ are concerned my own work is -only a confirmation and amplification of his, since Charybdea and -Tripedalia in this respect agree with Chiropsalmus.</p> - -<p>The vascular lamellæ of the internal system are the most prominent -and morphologically the most important. They comprise the four -vertical strips of fusion that separate the four stomach pockets in the -interradii (<i>ivl</i> in the figures of the series of cross-sections of Charybdea -and Tripedalia, Nos. <a href="#plate3">6-15</a> and <a href="#plate5">21-29</a>), and four curved horizontal cross-pieces -at the top of these which separate the stomach from the stomach -pockets, and would make the separation complete did they not leave in -each perradius a free space between their ends, which makes possible the -gastric ostia.</p> - -<p>The arrangement of this internal system of vascular lamellæ is -simple. What they amount to is a certain definite number of linear -adhesions between the two walls of an originally undivided gastro-vascular -space, by which that space is divided up into a central stomach -and a peripheral portion, and the peripheral portion thus further divided -into the four stomach pockets. Perhaps the idea may be conveyed by -likening the whole medusa to a couple of bowls fitting closely one within -another and plastered together at the margins. The exumbrella then -would correspond to the outer bowl, the subumbrella to the smaller inner -bowl, and the original undivided gastro-vascular space to the space -between the two. If now the walls of the space be cemented together in -four horizontal curved lines just in the plane where the bottoms are -bending round to become the sides of the bowls, leaving four interspaces -between the ends of the lines, we should have the original space divided -into a central horizontal somewhat lens-shaped region between the -bottoms of the two bowls that would correspond to the central stomach, -and a peripheral vertical portion between the sides of the bowls that -would correspond to the peripheral gastro-vascular system; central and -peripheral portions would communicate by the four interspaces between -the lines of fusion, which would correspond to the four gastric ostia. If, -further, the vertical peripheral portion be subdivided by four more lines -of fusion running vertically at equal distances apart, each connecting -above with the middle point of the corresponding horizontal line of -fusion, we should have the simple peripheral portion divided into four -parts, corresponding to the stomach pockets, by four vertical lines of -fusion, corresponding to the four interradial vascular lamellæ, the <i>ivl</i> of -the figures.</p> - -<p><span class="pagenum"><a name="Page_29" id="Page_29">[29]</a></span></p> - -<p>These mutual relations of stomach, stomach pockets and lamellæ -will perhaps be made clearer if a comparison is drawn between them -and the similar structures of a Hydromedusa. Liriope, one of the -Trachomedusæ, is a good form to take for such a comparison, since by -reason of its direct development from the egg it is free from the complications -of hydroid medusæ. The young medusa has at first a simple, -undivided gastro-vascular cavity which later is divided up into the -central stomach and the typical radial to circular canals of the Hydromedusæ -by means of fusions between the two endodermal surfaces. Diagrams -<i>a</i>, <i>b</i> and <i>c</i> of <a href="#plate8">Fig. 35</a> represent very schematically this process of -division into stomach and canals. In <i>a</i> we have a projection upon a -plane surface of the primary, undivided gastro-vascular cavity, as seen -from above; <i>b</i> shows the first four points of fusion in the interradii; -<i>c</i> represents those four points expanded by growth in all directions into -broad cathammal plates in such a way as to leave the stomach in the -centre, the radial canals in the perradii, and the circular canal in the -periphery as all that remains open of the primary simple cavity. These -broad plates of vascular lamella, separating the narrow radial canals, -persist in the adult Liriope to tell the tale of the formation of the definitive -gastro-vascular system. It seems to me that we are justified by -analogy in drawing a similar conclusion for the Cubomedusæ. In <i>d</i> of -<a href="#plate8">Fig. 35</a> is represented a projection of a Cubomedusa, in which the -homology of the stomach pockets with the radial canals of the Hydromedusa, -and of the narrow strips of fusion with the broad cathammal -plates, is shown at a glance. To make the comparison more perfect we -have only to remember that in the Cubomedusæ there exists below each -interradial vascular lamella a connecting canal (Figs. <a href="#plate4">16</a>, <a href="#plate6">29</a> and <a href="#plate8">35</a> <i>d</i>, <i>cc</i>) -uniting the two separate adjacent pockets. This, as has been pointed -out by other writers, is the representative of the circular canal of the -Hydromedusæ. Practically the only difference between the structure of -the gastro-vascular system of the Cubomedusæ and that of a form such -as Liriope, is that in the latter the fused areas have broadened out at the -expense of the radial canals, while in the Cubomedusæ on the contrary -they have become long and narrow.</p> - -<p>One is strongly tempted by the foregoing comparison to speculate a -little as to whether the reproductive organs of the Cubomedusæ, which -lie <em>in</em> the stomach pockets and are generally supposed to be endodermal, -may not bear some closer relation to those of the Trachomedusæ, which -lie “in the course of” the radial canals (Lang’s Text-book) and by common<span class="pagenum"><a name="Page_30" id="Page_30">[30]</a></span> -consent are ectodermal. And while we are being led by facts such as -those just mentioned above to wonder just a little whether after all the -position of the Cubomedusæ among the Acraspeda is so firmly assured—doubting -some, yet in the frame of mind of one who “fears a doubt as -wrong”—the velarium suggests itself as another point in question. -Haeckel does not hesitate to state emphatically that the velarium of the -Cubomedusæ and the velum of the Craspedote medusæ are only analogous, -but the reasons that he gives (sie sind unabhängig von einander -entstanden, und ihre Structur ist zwar ähnlich, aber keineswegs identisch; -namentlich das Verhalten zum Nervenring ist wesentlich verschieden: -System, p. 426) somehow do not produce so much impression -upon one as the very velum-like appearance of the velarium itself. The -origin from the fusion of marginal lobes is not as yet a matter of observation, -and the relation to the nerve ring is not essentially different from -that of the velum to the lower (<i>i. e.</i> inner) nerve ring in the Craspedotæ. -The four frenula and the diverticula from the gastro-vascular system -seem to be the chief differences in structure after all, and these Haeckel -evidently did not think worth mentioning. This speculation, as to the -possible relation of the Cubomedusæ to such forms of the veiled medusæ -as Liriope, though it may be very tempting, is scarcely fruitful enough -to repay much effort on the part of either reader or writer. The whole -subject must remain uncertain until the facts of the development of the -Cubomedusæ are known.</p> - -<p>If the structure of the vascular lamellæ of the internal system has -been made clear, the appearances of the vertical and horizontal components -in the figures will be understood without much further explanation. -The four vertical strips in the interradii (<i>ivl</i>) have been already -referred to in the figures of the cross-sections of both Charybdea and -Tripedalia. In the longitudinal sections of the two jelly-fish through the -interradii, the vertical lamellæ are cut throughout their entire length -from stomach to connecting canals (Figs. <a href="#plate2">5-20</a>, <i>ivl</i>). The horizontal -cross-pieces at the tops of the vertical lamellæ also appear in several of -the figures. <a href="#plate4">Fig. 36</a> represents the appearance that would be given by a -longitudinal section taken through any portion of the upper part of the -bell except in the interradii, or in the perradii, through the gastric ostia. -The horizontal vascular lamella (<i>hvl</i>) is shown connecting the endoderm -of the stomach (<i>ens</i>) with that of the stomach pocket (<i>enp</i>). In a longitudinal -section directly through an interradius (<a href="#plate2">Fig. 5 or 20</a>) the horizontal -lamella is cut just at the point where it joins the vertical, so that<span class="pagenum"><a name="Page_31" id="Page_31">[31]</a></span> -the two are not differentiated. In a section through the region of a perradius -(<a href="#plate2">Fig. 4 or 19</a>) the horizontal lamella is of course not cut, since the -section passes through the gastric ostium, whose existence is conditional -upon fusion not having taken place between the endodermal surfaces.</p> - -<p>The first figure in each of the series of cross-sections (Figs. <a href="#plate3">6</a> and <a href="#plate5">21</a>) -also shows the horizontal vascular lamella, cut across slantingly twice in -each quadrant as it passes between the gelatine of the ex- and of the subumbrella -to connect the epithelium of the stomach with that of the -stomach pocket. The fact that more of the lamella does not appear in -such a cross-section only shows that its course is not perfectly horizontal.</p> - -<p>The region in which the same lamella lies is indicated in the surface -view of the top of the bell of Charybdea (<a href="#plate1">Fig. 2</a>) by the bent line <i>hvl</i> in -each quadrant. The figure manifests the appropriateness of Claus’s -name for the horizontal lamella—“bogenförmige Verwachsungs-Streifen.” -Haeckel calls the same structures “Pylorus-Klappen,” and in -his account of Charybdea Murrayana in the Challenger Report, speaking -of the three divisions of the stomach (buccal, central and basal) which he -traces upwards from the stalked forms of Scyphomedusæ, he says: “The -central stomach in this Charybdea, as in most Charybdea, is joined to -the basal stomach, as the pyloric stricture between the two is not developed -and only faintly indicated by the slightly projecting pyloric valves.” -Again, in speaking of the valves of the gastric ostia, he says: “These -four perradial ‘pouch valves’ alternate with the interradial pyloric -valves.” It is difficult to understand, however, how the “bogenförmige -Verwachsungs-Streifen” of Claus, which are undoubtedly the same structures -as those which I have called the horizontal lamellæ, and are only -strips of endodermal fusion, can be “projecting pyloric valves,” or indeed -can properly be spoken of as valves at all. Possibly Haeckel was not -quite able to understand Claus’s description, and in his desire to find -something in the stomach of Charybdea which would serve to set off a -central from a basal part, such as is found in the Lucernaridæ, hit upon -Claus’s “Verwachsungs-Streifen.” I have elsewhere given it as my -opinion that in such of the Cubomedusæ as I have studied there is no -structure in evidence that would properly serve to mark a limit between -a basal and a central portion of the stomach.</p> - -<p>We have next to describe the marginal system. The vascular -lamellæ mentioned above in every case connected endoderm of one -cavity with endoderm of another; those of the margin have the noteworthy -difference that they run from endoderms of some part of the<span class="pagenum"><a name="Page_32" id="Page_32">[32]</a></span> -gastro-vascular system to <em>ectoderm of the surface</em>. The outermost cells of -the endodermal lamellæ make direct connection with the ectodermal -cells, without the usual intervention of a layer of gelatine.</p> - -<p>The marginal lamella of Charybdea lies, as the name implies, just on -the bell margin where the edge is curving round into the velarium. All -around the whole circumference of the bell it is found (in Charybdea) at -this same horizontal bend, except in the eight principal radii, where the -tentacles and the sensory clubs have brought about modifications. In -any place except these a vertical section through the margin will show -the marginal lamella connecting the endoderm of the marginal pocket -with the ectoderms of the surface, as represented by <i>vlm</i> in <a href="#plate4">Fig. 38</a>, which -is a vertical section through the sensory niche a little to one side of the -perradial axis.</p> - -<p>In the interradii the marginal lamella undergoes modifications due -to the fact that the bases of the pedalia are situated a little upwards -from the exact margin, and that the lamella follows the outline of the -bases. <a href="#plate1">Fig. 1</a> shows one of the interradial corners of the bell margin -looked at directly from the surface, so that the curved outline of the -junction of the base of the pedalium with the exumbrella is seen. The -trace made by the lamella where it meets the surface ectoderm follows -this outline. The lamella is also shown in the vertical section through -the interradius (<a href="#plate2">Fig. 5 or 20</a>, <i>vlm</i>), where it is seen running from the -connecting canals (<i>cc</i>), which joins the two adjacent marginal pockets, -upwards and outwards to meet the surface ectoderm. Its course from -canal to surface is not in a direct line, but curved with the concavity -upwards. Hence, in cross-sections at certain levels through the interradial -corner it is met more than once and gives rise to appearances that -seem at first sight too complicated for it to be just the same structure as -the simple marginal lamella described above. That it is the same, and -that the complication is only due to the insertion of the pedalia above -the margin, can be determined by following through a series of cross-sections, -the essential ones of which, as I hope, are given in <a href="#plate6">Figs. 40-43</a>. -The levels of these are shown on <a href="#plate2">Fig. 5</a> by the letters <i>w</i>, <i>x</i>, <i>y</i> and <i>z</i>, -respectively. <a href="#plate6">Fig. 40</a> shows the lamella cut but once, just below its highest -part. The section is above the level of the connecting canal and hence -still shows the vertical interradial lamella <i>ivl</i>. <a href="#plate6">Fig. 41</a>, at the next lower -level (<i>x</i>), shows the same portion of the lamella intersected a little nearer -the interior, while the junction with the endoderm of the connecting -canal is shown still further inside. <a href="#plate6">Fig. 42</a> is at level <i>y</i>, just through the<span class="pagenum"><a name="Page_33" id="Page_33">[33]</a></span> -bend of the loop, so that in part of its course the lamella is cut almost -horizontally, <i>i. e.</i> in its own plane. <a href="#plate6">Fig. 43</a> finally shows the lamella as -it appears below the level of the connecting canal, cut twice, each portion -joining endoderm of marginal pocket with ectoderm of surface. It thus -bears exactly the same relations that it had when we first met it in <a href="#plate4">Fig. -38</a> (<i>vlm</i>), except that here in <a href="#plate6">Fig. 43</a> one finds that a cross-section cuts it at -right angles instead of a vertical as in <a href="#plate4">Fig. 38</a>, as a result of its being -pushed upwards from its former position on the margin by the insertion -of the pedalium above the margin.</p> - -<p>The vascular lamella of the sensory niche has already been alluded to -as part of the marginal system, and brief reference has been made to it -in the section on the sensory clubs. Like the rest of the marginal -lamella, it connects endoderm with ectoderm. The line that its fusion -with the ectoderm traces on the surface frames in a shield-shaped area -at the bottom of the sensory niche, which is seen in the drawing of the -outlines of the niche, <a href="#plate6">Fig. 44</a> (<i>vls</i>). This lamella was observed by Claus, -and was figured by him both in surface view and in cross-section -through the niche. Apparently, however, he omitted vertical sections -through the niche, so that he supposed that the outline traced by the -lamella was not continuous above, <i>i. e.</i> over the stalk of the sensory club -(’78, Fig. 41; text, p. 28). That the outline is closed above, though -masked in surface view by the roof of the sensory niche, is seen at once -in vertical sections, such as <a href="#plate4">Figs. 37 and 38</a>, one of which is directly -through the perradius, the other a little to one side. Both show the vascular -lamella of the sensory niche (<i>vls</i>) intersected twice, above and below -the sensory club, and completely cutting off the exumbrella from any -share in the bottom (or inner wall) of the sensory niche. <a href="#plate4">Fig. 39</a>, which -is a cross-section through the upper part of the niche, and is essentially -like the similar figure of Claus, shows in like manner that the bottom of -the sensory niche belongs to the subumbrella. H. V. Wilson was the -first to point out, in his unpublished notes, that the lamella of the niche -is complete all round.</p> - -<p>In the adult structure of Charybdea and Tripedalia the lamella of -the niche is connected with that of the margin by a vertical strip of -endodermal fusion that does not come to the surface like the rest of the -marginal system, but remains just internal to the gelatine of the exumbrella, -connecting the two adjacent marginal pockets. In the cross-sections -of Charybdea it is seen in <a href="#plate4">Fig. 16</a> (<i>vlc</i>); in those of Tripedalia it -is seen in <a href="#plate6">Figs. 28 and 29</a>. In vertical section it is found in Figs. <a href="#plate2">4</a>, <a href="#plate2">19</a><span class="pagenum"><a name="Page_34" id="Page_34">[34]</a></span> -and <a href="#plate4">37</a>. In <a href="#plate6">Fig. 44</a>, which represents the bell margin and velarium of -Tripedalia arranged as if the velarium were vertical and pendant from -the margin (instead of suspended by the frenulum so as to be at right -angles to the vertical plane), the connecting lamella is shown as a dotted -line (<i>vlc</i>)—dotted because it does not come to the surface—joining the -lamella of the niche with that of the margin (<i>vlm</i>).</p> - -<p>The same figure (<a href="#plate6">No. 44</a>) shows a characteristic difference between -the marginal lamella of Tripedalia and that of Charybdea. While in -Charybdea, as Claus points out, the marginal lamella keeps at one level, -just a little above the bell margin, all the way round (except where disturbed -by the special modifications of the tentacles and the sensory -clubs), and never descends into the velarium, in Tripedalia on the other -hand it describes a sinuous course, following the outlines of the marginal -pockets, as is indicated in the figure by the light parallel line <i>vlm</i>. -The course as it would be seen in a surface view is obscured just at each -side of the interradius by the overhanging of the bases of the two lateral -pedalia. This is why the lamella is not indicated at these points in the -diagram. The course is seen to lie almost wholly on the velarium, that -is, in the figure below the line which represents the bell margin proper, -the line at which the angle comes when the velarium is in its normal -position, horizontal to the vertical side of the bell.</p> - -<p>In this sinuous course of the marginal lamella we have another point -of resemblance between Tripedalia and the Chirodropidæ. H. V. Wilson -worked it out in his sections of Chiropsalmus, and the reconstruction -which I have given in the figure under discussion is in all essentials -similar to his for Chiropsalmus. The differences lie only in the fact that -Chiropsalmus has more velar canals, and that the chief marginal pocket -in each quadrant is not forked peripherally, as is that of Tripedalia (<i>mp</i>), -but presents its distal margin parallel to the edge of the velarium. The -two smaller marginal pockets in the perradii (<i>mp´</i>) are on identically the -same plan in both.</p> - -<p>Tripedalia, having three tentacles joining the umbrella in each interradius, -shows a disturbance of the course of the marginal lamella in -these regions by just so much the more complicated than in Charybdea. -The plan, however, is exactly the same. The lamella is pushed upwards -from the margin by each of the bases of the three pedalia just as is done -by the base of the single pedalium of Charybdea. <a href="#plate6">Fig. 29</a> shows the -lamella in the same relation to the canal of the central tentacle (<i>ct</i>) that -it has in the similar sections of Charybdea (Figs. <a href="#plate4">16</a> and <a href="#plate6">43</a>); and in<span class="pagenum"><a name="Page_35" id="Page_35">[35]</a></span> -addition the first appearances (as the series is traced downwards) of the -arches of the lamella over the two lateral tentacles (<i>ct´</i>), which are -inserted a little lower down than the middle one of the group. As concerns -these lateral tentacles, the relations of the vascular lamella at this -level are the same as that in the level of <a href="#plate6">Fig. 40</a> for Charybdea.</p> - -<p>It has been stated more than once already that the vascular lamella -of the sensory niche is a part of the lamella that runs round the margin, -and so far the only evidence given has been the strip of endodermal -fusion running from the marginal lamella to that of the niche. This -strip, however, as has been described, does not come to the surface and -consequently seems at first sight to be a different structure from the -lamella of the margin. That it is not, however, I found very prettily -shown in a series of sections of one of my youngest Tripedalia. In this -the lamella of the niche as it was traced in successive sections downwards, -was found not to form a closed ring at the bottom of the niche, but each -side was continued directly and separately downwards to the margin, -where it passed into the corresponding part of the marginal lamella. A -reconstruction of the condition, similar to that of <a href="#plate6">Fig. 44</a>, is given in <a href="#plate6">Fig. -45</a>, and I think explains itself at a glance. Evidently the vascular -lamellæ that connect the lamella of the sensory niche with that of the -margin at first come to the surface, like the rest of the marginal system, -but as the animal grows older come to lie within the gelatine. In this -way the condition found in cross-sections just through the margin of my -very small Tripedalia, and represented in <a href="#plate6">Fig. 46</a>, becomes that of the -adult seen in the corresponding portion of <a href="#plate6">Fig. 29</a>. It is as complete a -demonstration as could be required that the lamella of the sensory niche -is at first only a loop of the marginal lamella, a conclusion that had been -already reached by H. V. Wilson on theoretical considerations, based -upon the facts of the adult structure as he found them in Chiropsalmus.</p> - -<p>As Wilson pointed out in his notes, these facts have a close bearing -upon the question of the origin of the velarium. Sixteen marginal -pockets are found in both Chiropsalmus and Tripedalia, and all of them -extend into the velarium. It is not unnatural to suppose that these -belong to sixteen marginal lobes, and that these lobes have fused together -to form the velarium. In the Chirodropus figured by Haeckel (Taf. -XXVI) in his “System” gelatinous lobe-like thickenings are shown in -the velarium, corresponding to the sixteen marginal pockets. In Tripedalia -no special gelatinous thickenings are found, but the arrangement -of the marginal pockets is the same as that of the Chirodropidæ, and<span class="pagenum"><a name="Page_36" id="Page_36">[36]</a></span> -perhaps I ought, when treating of the systematic relations of Tripedalia -(<a href="#Page_5">p. 5</a>, Fam. III), to have recognized the analogy to the extent of saying -that marginal lobes may not be completely absent from the velarium of -Tripedalia. At any rate the gelatinous lobes in the case of Chirodropus on -the one hand, and on the other hand the sinuous outline of the margin -still mapped out by the lamella in Chirodropus, Chiropsalmus and Tripedalia, -are certainly very suggestive of an ancestral Cubomedusa in which -there was no velarium, but sixteen free marginal lobes instead. Two -more indications favor slightly the same view. In both Charybdea and -Tripedalia a small notch is seen in the edge of the velarium in the perradius -(<a href="#plate6">Fig. 44</a>). Its constancy suggests that it may not be a chance or -meaningless feature. The second point is the small size of the two -marginal pockets adjoining the perradius. These are in the position of -the ephyra lobes of the Discomedusæ, which always lie on either side of -each sensory club, and which do not keep pace with the other marginal -lobes in development. In the Rhizostome jelly-fish especially they are -found much smaller than the other lobes, as will be seen by a glance at -such figures as Haeckel’s for Lychnorhiza (System, Taf. XXXIV Fig. 2), -or for Archirhiza (Taf. XXXVI, Fig. 5), or Hesse’s figure of the margin -of Rhizostoma Cuvieri (’95, Taf. XXII, Fig. 22). The resemblance between -such margins and that of Tripedalia (<a href="#plate6">Fig. 44</a>), with its simple, unbranched -velar canals, is very suggestive. On the other hand it must be remembered -that in considering the vascular lamellæ of the internal system we -found the indication pointing rather more to Hydromedusan affinities -than to any other. Charybdea throws no light on the question, since it -has no marginal lobes on the velarium and the marginal pockets end -strictly at the margin, so that the only diverticula of the gastro-vascular -system in the velarium are the velar canals.</p> - -<p>Before leaving the subject of marginal lobes and pockets I must -answer a possible objection that may occur to some careful reader. It -may seem that I am wrong in holding that there are two marginal -pockets in each octant instead of three, that just as there is one velar -canal from each of the smaller perradial pockets (<i>mp´</i>, <a href="#plate6">Fig. 44</a>), so each -prong of the forked larger pocket (<i>mp</i>), since it is continued into a velar -canal, ought to be called a marginal pocket likewise, the whole number -of marginal pockets then being twenty-four instead of sixteen. Such a -revision of the terminology would not be without some reason in its favor, -and perhaps a study of more forms would show it to be correct. But for -the present, at any rate, it seemed to me best to abide by the analogy of<span class="pagenum"><a name="Page_37" id="Page_37">[37]</a></span> -Chiropsalmus, in which the peripheral edge of the larger marginal pocket -in each octant is not bow-shaped, but runs parallel to the edge of the -velarium. A revision of the terminology of the marginal pockets such -as implied in the suggestion above would also give rise to complications -when applied to Charybdea, since the latter has no marginal pockets in -the velarium.</p> - -<p>As to the functions of the vascular lamellæ, there is too little known -to say much. It is rather improbable that structures retained so definitely -should be mere scaffolding left over from a previous stage of -usefulness. Claus has found in Chrysaora that the lamellæ form a kind -of capillary network in communication with the gastro-vascular system, -and he with others supports the view that they perform an accessory -function in the nutrition of the tissues they penetrate. Upon this point -I have no observations of my own to add.</p> - -<p>The marginal vascular lamella is regarded by Claus as perhaps the -vestige of a circular canal around the bell margin. On this subject, too, -I have nothing to add. A lamella of endoderm that connects directly -with the ectoderm of the surface along its whole course is a structure -whose meaning I am wholly unable to understand or even to guess at. -A similar lamella is described by Hesse (’95, p. 430) as occurring in the -ephyra lobes of his Rhizostoma, and he mentions Eimer as the first to -discover this structure, probably meaning the first to discover it in the -Discomedusæ. Whether the lamella is found all around the margin is -not stated. Hesse refers it to the ephyra, and remarks that the investigation -of it in the ephyra would undoubtedly give interesting results.</p> - -<p>I will close this part upon the vascular lamellæ with a very pertinent -suggestion made by Professor Brooks to the effect that the usual way of -speaking of the sensory clubs as having moved up from the margin is -looking at the matter in the wrong way. The level of the sensory clubs -undoubtedly represents the original margin, which elsewhere has grown -down and away from its former level, leaving the sensory clubs like -floatage stranded at high-tide mark. Only in this way can the lamella -of the sensory niche have any meaning.</p> - -<h3>B: <span class="smcap">The Nervous System.</span></h3> - -<p>The nervous system of the Cubomedusæ is the most highly developed -that is found in any of the jelly-fishes. If the position of the group -among the Acraspeda is established, it alone is ample to prove that the -Hertwigs had not sufficient evidence when they stated in their monograph<span class="pagenum"><a name="Page_38" id="Page_38">[38]</a></span> -on the nervous system of the Medusæ (’78) that the Acraspeda -show a much lower nervous organization than the Craspedota.</p> - -<p>The system naturally groups itself under three heads, the nerve -ring, the sensory clubs, and the motor plexus of fibres and ganglia that -underlies the epithelium of the subumbrella. The general relations of -the nerve ring and of the sensory clubs have been given before in the -description of Charybdea Xaymacana, so that we may pass at once to the -consideration of the finer details of the nervous tissues.</p> - -<p>In the structure of the nerve ring I have found myself unable to -come to the same results as those given by Claus, who so far as I know -is the only one that has studied the nerve with special reference to its -histology. Our difference amounts to this, that he finds two distinct -types of cells in the epithelium of the nerve, sensory and supporting, -which would make it a receiving as well as transmitting organ, while I -have not been able to demonstrate satisfactorily the sensory cells, and, -therefore, so far as my own observation is concerned, I am disposed to -attribute to the nerve simply the function of conducting impulses. I do -not know just how much weight to assign to my inability to find -evidence in my sections of the sensory type of cells. Eimer (mentioned by -Hesse, ’95, p. 420), the Hertwigs (’78) and Claus (’78) have independently discovered -the two types in one medusa or another, and the Hertwigs, at least, -have demonstrated them by macerated preparations. So far as Charybdea -is concerned, however, Claus had only preserved material and had to rely -upon sections, as have I, since the material which I had preserved with -especial reference to maceration did not turn out well. The results that -we get from sections vary enough for me to believe that Claus interpreted -his sections very much by analogy with other forms—as indeed, -is suggested by his own words (’78, p. 22): “Da es mir nicht geglückt ist -die durch die längere Conservirung in Weingeist fest vereinigten -Elemente zu isoliren, habe ich das muthmassliche Verhältniss beider -Elemente nach Analogie der mir für die Acalephen bekannt gewordenen -Verhältnisse, welche O. und R. Hertwig so schön auch am Nervenring -der Carmarina zur Darstellung gebracht haben, zu ergänzen versucht.” -There can be no doubt of our having the same structures to deal with, -for C. Xaymacana is so much like C. marsupialis as to be perhaps more -worthy of being called a variety of the latter than a distinct species.</p> - -<p>The structure of the nerve as I conceive it is given in <a href="#plate7">Figs. 47 and -48</a>. The former represents a cross-section, and shows, as others have -pointed out, that the layer of circular muscle fibres (<i>cm</i>) is interrupted by<span class="pagenum"><a name="Page_39" id="Page_39">[39]</a></span> -the nerve. It is evident that the tissues which elsewhere on the subumbrella -were differentiated into muscle epithelium and muscle fibre have -here become nerve epithelium and nerve fibre, a point that has not been -remarked upon before, so far as I remember, and that may be of interest -in connection with the neuro-muscular theory. The epithelium of the -nerve (<i>scn</i>) is seen to be made up of cells whose inner ends narrow down -into a kind of stalk or process that runs to the gelatine of the supporting -lamella (<i>gs</i>) and there joins a little cone of the gelatine that juts out to -meet it. The cells are smaller in general than those that overlie the -muscle layer, especially on the two lateral margins of the nerve, where -they are more crowded together and overarch the nerve-fibres. The -fibres are seen in cross-section between the processes of the cells. They -apparently must lie imbedded in some clear, watery fluid that does not -show in the preserved material. The processes of the epithelial cells -give the fibres the appearance of lying in alveoli, or being divided into -strands, and one of these strands (<i>ax</i>) is always discernible among the -others by reason of its more numerous or finer or more compactly -massed fibres. This is the “axis” of Claus. Here and there in its course -appear ganglion cells having their long axis in the longitudinal direction -of the nerve. Elsewhere, in the nerve as well, and usually nearer to the -surface, are found other ganglion cells, mostly bipolar, some multipolar, -which are readily distinguishable from those of the axis by the fact that -their long axis lies across the nerve. One of these cells is shown in the -figure (<i>gc</i>). Here and there in the epithelium alongside the nerve are -found mucous cells (<i>mc</i>), distinguished by their clear contents and by the -small exhausted-appearing nucleus at the base with a few threads of -protoplasm.</p> - -<p>In <a href="#plate7">Fig. 48</a> I have tried to represent the structure of the nerve by -means of a series of five different views such as would be given by -focusing at five successive levels. In the first (1) we have the epithelium -of the nerve (<i>scn</i> in <a href="#plate7">Fig. 47</a>) in surface view, the cells appearing -polygonal in outline, with here and there a mucous cell. In (2) we find a -very slight layer of ganglion cells and fibres having a transverse direction -(<i>gc</i> and <i>fp</i> in <a href="#plate7">Fig. 47</a>). These are continuous with the plexus of fibres and -ganglion cells which lie above the muscle layer all over the subumbrella, -and which represent the motor part of the nervous system. This connection -with the nerve shows how co-ordination is effected. At the same -level are found fibres of the axis also having a longitudinal direction. -In (3) is seen the main body of fibres, divided in the osmic preparation<span class="pagenum"><a name="Page_40" id="Page_40">[40]</a></span> -from which the drawing was made into irregular wavy strands which -are in all probability largely the result of preservation, but are in part -also due to the separation by processes of the epithelial cells, as was seen -in <a href="#plate7">Fig. 47</a>. The axis is seen with one of its longitudinally directed bipolar -ganglion cells; and at the sides the fibres of the circular muscle of the -subumbrella. These show a slanting direction to the nerve, due to the -fact that the nerve, as mentioned before, has a sinuous course from the -margin in interradius to the level of sensory club in perradius. At the -next focus (4) we come to the gelatine of the subumbrella (<i>gs</i> in <a href="#plate7">Fig. 47</a>), -and below this (5) to the larger polygonal outlines of the endodermal -cells of the stomach pocket (<i>enp</i>, <a href="#plate7">Fig. 47</a>), which like the ectoderm show -mucous cells at irregular intervals.</p> - -<p>A comparison, now, with Claus’s figures (’78, Taf. II, Figs. 19-21) will -show that, except for the rather unimportant matter of the mucous cells, -which he finds regularly and thickly disposed on each side of the nerve -(’78, Fig. 21), our only essential difference lies in the matter of sensory -cells in the epithelium. His figures show a multitude of spindle-shaped -sensory cells whose central ends are continued in processes that bend -around into the mass of fibres of the nerve. In his Fig. 20 a relatively -small number of nuclei, just one-third as many, are seen attached nearer -to the surface, which represent the supporting cells. The plan of structure -(as shown in his Fig. 20) is an alternation of (1) supporting cells -offering a broad peripheral end to the surface and having the central end -continued as a supporting fibre to the gelatinous lamella, and (2) spindle-shaped -sensory cells with nuclei at a lower level, which send their -peripheral process up between the supporting cells to the surface, while -the central process becomes continuous with the nerve fibres, often -branching into two processes. In my sections I have not been able to -see either a regular alternation of nuclei at different levels, or central -processes which unmistakably bend round into the nerve fibres. In -every case in which I could trace the central process of a cell clearly it -ran to the supporting lamella, and this whether the nucleus of the cell -lay near the surface of the nerve or deeper down, as in the somewhat -spindle-shaped cell seen on the left of the centre of the nerve in <a href="#plate7">Fig. 47</a>. -Of course in many cases the central process could not be traced in a -section, and this leaves room for the supposition that such were always -the sensory cells. From my inability to demonstrate sensory cells in the -nerves of Charybdea, I by no means wish to deny their existence; for -that remains to be proved, or disproved, by macerations. At any rate,<span class="pagenum"><a name="Page_41" id="Page_41">[41]</a></span> -they cannot be so numerous as has been supposed. The position of the -nuclei shows that.</p> - -<p>The epithelium of the nerve is said by Claus to be ciliated. It has -been suggested by Schewiakoff that probably in such cases the sensory -cells bear one long cilium, while the supporting cells have many smaller -cilia. Unfortunately, I made no observations upon the ciliation of the -nervous structures of the living animal, and the traces of cilia that are -shown in preparations of preserved material are a poor basis to speculate -much on. Claus considers the sensory cells of the epithelium of the -nerve a special seat of tactile sensation.</p> - -<p>The way in which the nerve reaches the sensory clubs is interesting. -Under the topic of the vascular lamellæ it was explained that the sensory -clubs and the bottom of the sensory niche from which they spring are -parts of the subumbrella. <a href="#plate4">Fig. 37</a> reminds at a glance better than any -other one drawing how the bottom or inner wall of the niche is completely -cut off from the exumbrella by vascular lamellæ above and below -the stalk of the club. From this figure, now, it will readily be understood -that the nerve in order to pass to the base of the stalk has simply -to traverse the gelatine of the subumbrella. This fact, which seems surprising -enough at first sight in view of the position of the clubs on the -external surface of the umbrella, was correctly pointed out and explained -by Claus, but one or two figures will serve perhaps to give a clearer -idea of it.</p> - -<p><a href="#plate7">Fig. 49</a> is a diagram of the nervous structures in the region of the -sensory niche, as they would be seen on the surface of the subumbrella -turned toward the bell cavity. The outline of the sensory niche as it is -seen through the tissue of the animal is represented by the line <i>osn</i>. -The sensory club (<i>scl</i>), and its stalk with a conical basal portion are given -by the lightly dotted outline and are also imagined as seen through the -animal. The nerve (<i>n</i>), being on the surface of the subumbrella, is shown -as a heavy line describing an arch over the outline of the niche. In the -middle point of the arch is a slight thickening of the nervous tissue (<i>rg</i>) -which shows in section a large increase in the number of ganglion cells, -and is the radial ganglion of Claus. The same is seen, exaggerated in -size, in <a href="#plate3">Fig. 12</a>. From it there extends upward a slender strand of -nervous tissue (<i>rn</i>), the radial nerve of Claus. In Charybdea this can -be traced but a very short distance. In Tripedalia it is much more -distinct and traceable for a longer distance, and I might say in passing -that this and the sensory organs in the proboscis are the only differences<span class="pagenum"><a name="Page_42" id="Page_42">[42]</a></span> -I have noted between the nervous systems of Tripedalia and -Charybdea.</p> - -<p>Nerve ring, radial ganglion and radial nerve all lie on the bell cavity -surface of the subumbrella. The way, now, in which the nerve ring -reaches the base of the stalk is simply by sending two roots through the -gelatine of the subumbrella to the conical base of the stalk. These roots -are seen in the diagram at <i>rns</i>. After passing through the gelatine the -roots come together on the inner side of the base—that is, the side turned -toward the bell cavity—and then pass downwards (<i>nst</i>) on the inner side -of the stalk of the club to the mass of nervous tissue at its end.</p> - -<p>This passage of nervous tissue through the gelatine in order to reach -the sensory club is a little hard to grasp at the first, and I have tried to -render it more intelligible by a couple of drawings of sections. <a href="#plate7">Fig. 50</a> is -a transverse section through the upper part of the region of the sensory -niche, not quite horizontal (<i>i. e.</i> parallel with the bell margin), but slanting -so as to lie on the plane of the reference arrow <i>x-y</i> in <a href="#plate7">Fig. 49</a>. The -plane passes just through the top of the niche, and in two areas has cut -through the roof with its epithelium of ectoderm (<i>ece</i>, <i>ecs</i>) so that the -space of the sensory niche (<i>sn</i>) appears. The vascular lamella of the -sensory niche (<i>vls</i>) is shown, as in Figs. <a href="#plate3">13</a> and <a href="#plate4">14</a>, running on each side -from the endoderm that lines the canal of the sensory club (<i>enc</i>) to the -endoderm of the adjacent stomach pocket (<i>enp</i>). By it the gelatine -of the exumbrella is separated from that of the subumbrella, and -one sees that it is only through the latter that the nerve has to pass in -order to reach the base of the sensory club. It is also seen that one part -of the roof of the niche which is cut through lies outside of the ring of -lamella and is therefore lined with ectoderm of the exumbrella (<i>ece</i>) -while the other lies within the ring and is lined with ectoderm of the -subumbrella (<i>ecs</i>). Owing to the slanting direction of the cut only the -root on one side is cut through. The other is indicated, however, on the -right side of the drawing. In this method of passage of nerve fibres, -together with the accompanying ganglion cells, directly through the gelatine -to the stalk of the sensory club my work is only confirmation and -explanation of Claus.</p> - -<p><a href="#plate7">Fig. 51</a> is a vertical section through the base of the stalk in the -plane of the reference arrow <i>w-z</i> in <a href="#plate7">Fig. 49</a>, and therefore passing -through one of the roots of the nerve of the stalk. Here again the -region is seen to be cut off from the exumbrella by the vascular lamella of -the sensory niche (<i>vls</i>), and the nerve is seen passing through the gelatine<span class="pagenum"><a name="Page_43" id="Page_43">[43]</a></span> -of the subumbrella from the surface of the bell cavity (<i>sc</i>) to the base of -the stalk hanging in the sensory niche (<i>sn</i>). One of the ganglion cells -(<i>gc</i>) that accompany the nerve is seen to have two nuclei, a not infrequent -occurrence which has been pointed out by others.</p> - -<p>The same figure shows that the axis (<i>ax</i>) of the nerve has penetrated -the gelatine with the other fibres. Here at the base of the stalk it takes -a horizontal course and becomes directly continuous with the similar -structure of the other root, as Wilson, I believe, first pointed out. This -part of the nervous tract which runs horizontally along the base of the -stalk between the two roots (<a href="#plate7">Fig. 49</a>, <i>rns</i>) has been considered by Claus -the representative in Charybdea of the upper nerve ring of the Craspedota, -which therefore exists in Charybdea in four separate portions. Seeing, -however, that the region in which it is found belongs to the subumbrella, -the homology seems very doubtful. Moreover, the fact that the axis of -the nerve ring runs through this outer portion, instead of remaining on -the inner surface of the subumbrella and passing to the radial ganglion, -rather indicates that the outer portion is part of the original course of -the nerve ring, while the portion that remains on the inner surface is -perhaps a later formation.</p> - -<p>A very interesting feature of the nervous system occurs in the same -region in the form of a tract of fibres underlying the endoderm, and -separated from the other fibres by the gelatine of the supporting lamella. -It is seen in vertical section in <a href="#plate7">Fig. 52</a> (<i>enf</i>), which is a section through -the base of the stalk in just about its median plane, and, therefore, to one -side of the arrow <i>w-z</i> in <a href="#plate7">Fig. 49</a> and the corresponding drawing, <a href="#plate7">Fig. 51</a>. -In cross-section it is represented also in <a href="#plate7">Fig. 50</a> (<i>enf</i>). It varies in size -and prominence very much in different specimens. <a href="#plate7">Fig. 52</a> is a camera -drawing of it in the case that showed it most developed. Ganglion cells -are found in it, but comparatively infrequently. In some cases the tract -itself can hardly be found with certainty. Hesse has described in a -Rhizostome a much more highly developed tract in a corresponding -position on the base of the marginal body. Fibres from the “outer -sensory pit” pass through the gelatine to the sub-endodermal tract, -which is described as surrounding the epithelium of the canal of the -marginal body like a collar and is most thickly developed on the under -surface of the canal, at the place that just corresponds with the point -where, and where only, I find the tract in Charybdea. Hesse thinks that -fibres then pass from this region to the nervous epithelium of the “inner -sensory pit” lying underneath the base of the marginal body, which<span class="pagenum"><a name="Page_44" id="Page_44">[44]</a></span> -contains a rich supply of ganglion cells and is considered by him to be -the centre of the nervous system of the medusa. A close comparison -cannot be drawn with Charybdea in this matter, however, since Charybdea -has nothing to correspond with the “outer” and “inner” sensory pits. -Moreover, the endodermal tract is not found encircling the canal of the -sensory club, nor could I trace fibres passing from it through the -supporting lamella into the fibres of the nerves.</p> - -<p>Claus has figured (’78, Taf. V, Fig. 45, <i>Fb</i>) a small bundle of fibres in -the stock of the sensory club lying between the endoderm cells of the -canal and the supporting lamella. The same bundle is found in both -Charybdea and Tripedalia and can be traced in cross-sections up the -stalk to a point which must correspond with that at which the endodermal -tract is seen in <a href="#plate7">Fig. 52</a>. Downwards it can be traced only as far as -the entrance of the stalk into the knob of the club where it invariably -becomes lost to view. According to Hesse (’95, p. 427) Schäfer found -under the endoderm cells of the whole stalk of the marginal body a -fibrous layer like that under the endoderm cells which he refers to -slender processes from the cells of the crystalline sac. Although Hesse, -as we have seen, finds the layer more limited in extent than Schäfer -gives it, and does not trace it to the same source, the observation of -Schäfer seems to me worthy of mention here, inasmuch as the trend of -the fibrous bundle under the endoderm cells of the stalk in Charybdea -and Tripedalia suggests quite strongly that the fibres come from the -crystalline sac, as Schäfer thought to be the case in his medusa.</p> - -<p>Besides the radial ganglion situated in the course of the nerve ring -at its four perradial points there are four other similar ganglia on the -subumbrella. These lie in the interradii, at the four lowermost points of -the nerve’s course, and undoubtedly send off nerves into the pedalia at -whose bases they are situated. F. Müller (’59), whose work was not -accessible to me, is quoted by Claus as recording two ganglia opposite -the base of each pedalium which gave off a great number of nerves -partly into the velarium, partly into the tentacles. Claus observed -nothing of the kind in Charybdea and states that even the interradial -ganglia do not exist.</p> - -<p>That they do, however, is shown without doubt in sections of both -C. Xaymacana and Tripedalia, but nerves to the velarium or to the tentacles -I was unable to find.</p> - -<p>On the two sides of each frenulum and of each suspensorium are -found subepithelial ganglion cells in greater numbers than elsewhere on<span class="pagenum"><a name="Page_45" id="Page_45">[45]</a></span> -the subumbrella, and I am inclined to ascribe to them also the importance -of special ganglia controlling the musculature of the frenula and -suspensoria. Certainly such ganglia would not be out of place.</p> - -<p>It has been mentioned that the greater prominence of the radial -nerve and the possession of special sensory organs in the proboscis were -the only points of difference I had noted between the nervous systems of -Charybdea and Tripedalia. These sensory organs remain to be described. -They are simple ciliated cysts containing a concretionary mass, and are -situated in the gelatine of the proboscis, irregularly disposed of at any -level, from the lips to the beginning of the stomach, and in any radius. -In one series of the adult animal fifteen were counted, of which seven -were situated about interradially, four perradially, two adradially and -two subradially. In another, twenty-one were counted, twelve in the -perradii and nine situated between the sub-and perradii. The one -shown in <a href="#plate5">Fig. 24</a> is in the perradial position, often seen. In the sections of -the very young Tripedalia in which the vascular lamella had not reached -the adult condition the sensory organs of the proboscis were not found, -although the sensory clubs showed practically no difference from the -adult. Their structure is very simple—merely a round or oval sac lined -with ciliated cells which bear up and keep in constant motion an irregular -coarsely granular concretion. <a href="#plate4">Fig. 53</a> is a sketch made in Jamaica -from the living specimen. Sections were somewhat disappointing in -that they added but little. <a href="#plate4">Fig. 55</a> was drawn to show that now and -then a mucous cell (<i>mc</i>) is found among the other cells of the sensory -epithelium. An irregular-shaped mass (<i>rc</i>) was always found inside the -cysts as the organic remains of the concretion. It gave no trace of -cellular structure and offered no evidence whether the concretion was -the product of one or few or of all the cells of the cyst. The latter would -be unique among the medusæ. Even if the otocyst is the result of the -activity of only one or a few cells, it is, so far as I know, the only case -known for the jelly-fish of a free, unsuspended concretion.</p> - -<p>As to whether the cysts are of ectodermal or endodermal origin -could not be determined, but there was some evidence in favor of the -latter. <a href="#plate3">Fig. 56</a> is a drawing of one seen in optical section in a whole -mount of part of a proboscis, and shows a definite connection with the -endoderm of the proboscis. This was the only case when such connection -was satisfactorily established, but in sections it was not uncommon -to find what seemed to be the remains of the broken stalk, as in <a href="#plate4">Fig. 54</a> -(<i>rs?</i>). No connection could be traced between the cysts and any other<span class="pagenum"><a name="Page_46" id="Page_46">[46]</a></span> -part of the nervous system. As to function, the idea that they serve to -give perception of space relations suggests itself as readily as any other -hypothesis.</p> - -<p>We come now to the consideration of the terminal knob of the clubs, -the sensory portion proper. A complete and detailed account of the -complex structure of these organs would fill many pages and involve -much useless repetition. Claus (’78) has described them with accuracy, -but not in great detail, and since then Schewiakoff (’89) has given a -careful general description and has supplemented Claus’s work by -observations upon the finer structure made with the aid of more recent -technique. It seems in place for me, therefore, to give in the briefest -possible way a general idea of their structure, and to pass then at once to -the points in which my work has led me to different conclusions from -those of Claus and Schewiakoff. In brief, then, the knob of the sensory -club consists of a thick, complex mass of nerve fibres, more or less -imbedded in which lie the special sensory organs, surrounding the -ampulla-like terminal enlargement of the canal. The surface between -the special organs is covered with less specialized sensory epithelium. -The sensory organs are seven in number. Of these, four are simple -invaginations of the surface epithelium arranged in two pairs symmetrically -to the median line in the proximal end of the knob (the end where -the stalk enters) and having pigment developed in the cells so invaginated, -while the space of the invagination is filled with a gelatinous refracting -secretion. These are considered simple eyes. Two more of the organs -are complex eyes situated on the median line of the inner surface of the -knob, the upper one smaller than the lower, but having almost exactly -the same structure. Each has a cellular lens over which extends a superficial, -corneal layer of cells; below the lens a refractive “vitreous body”; -and below this a retina with pigmented cells. The seventh organ is the -crystalline sac, which lies almost at the end of the knob opposite to the -stalk and contains a large concretion. In view of the fact that the -sensory clubs <i lang="la">in toto</i> have been abundantly figured by Claus and -Schewiakoff, it is my intention to give but one simple figure of the -general relations, and I justify that one in that it was made from the fresh -material. <a href="#plate3">Fig. 57</a> is a camera sketch of the outlines given by a sensory -club seen in optical section from the side. The smaller upper and the -larger lower complex eyes which are situated on the mid-line, are seen in -profile, while the two small simple eyes give the outlines that they would -in a surface view of their side of the knob. Of course it is understood<span class="pagenum"><a name="Page_47" id="Page_47">[47]</a></span> -that two similar ones would appear on the other side, since the four -simple eyes are symmetrically paired on either side of the mid-line. The -sketch seems to show at least this much, that even in the living state the -lens of the larger eye projects out beyond the other contours of the -surface, so that the marked convexity ascribed to it in descriptions is not -to be attributed to the preservation.</p> - -<p>It is in reference to the structure of the retina and vitreous body of -the complex eyes that I have found myself unable to come to the same -conclusions as Claus and Schewiakoff. Since the work of the latter goes -much further into the detail of the subject than does Claus’s paper, it -will be sufficient for me to compare my results simply with those of -Schewiakoff.</p> - -<p>The latter finds that the retina is composed of two kinds of cells, -corresponding to the supporting and sensory cells referred to in the -description of the nerve ring. These he figures (’89, Taf. II, Figs. 12 and -13) as alternating regularly. The two kinds of cells differ as follows:</p> - -<p>(1) Shape. The supporting cells like those referred to before, are -cone-shaped, having a proximal fibrous process that runs into the underlying -stratum of nerve fibres, and on the surface of the retina a broad -distal pigmented termination. The sensory cells are spindle-shaped, the -proximal processes becoming continuous with fibres of the underlying -nervous mass, while the distal process runs up to the surface of the -retina (the part toward the lens) in between the ends of the supporting -cell. The two kinds of cells are accordingly designated as pigment and -visual.</p> - -<p>(2) Position of nucleus. This comes in as a corollary of the shape. -The nuclei of the visual cells lie in the enlarged central part of the -spindle-shape, and, therefore, at a lower level than the nuclei of the -alternating pigment cells.</p> - -<p>(3) Processes in the vitreous body. The distal processes of the spindle-shaped -visual cells are continued through the vitreous body to the cells -of the lens as rod-like visual fibres which lie in canals in the (supposedly) -homogeneous vitreous body. The pigment cells on the other hand have -no fibres passing from them through the vitreous body, but in the latter -are situated cone-shaped masses of pigment whose bases rest upon the -broad ends of the pigment cells without, however, being a part of the -cell.</p> - -<p>(4) Pigment. The distal ends of the pigment cells in the retina are -strongly pigmented, as the name implies. The processes of the visual<span class="pagenum"><a name="Page_48" id="Page_48">[48]</a></span> -cells, which alternate with these, are pigmented likewise, but the pigment -is not so abundant and lies in the periphery of the cell body, leaving free -a highly refracting central axis.</p> - -<p>If the relation of these cells to each other has been made sufficiently -clear, it will be understood that, in accordance with Schewiakoff’s scheme -of the structure, sections that cut the retinal cells transversely give very -different appearances at different levels. A section through the very -tops of the retinal cells, that is, the last section of the retina before -striking the vitreous body, would show large polygonal areas of heavy -pigment (the ends of the pigment cells), in between which would lie the -much smaller, less pigmented, highly refracting ends of the visual cells -(’89, Taf. II, Fig. 19). A section lower down in the retina, that is, more -toward the centre of the club, would strike the low-lying enlarged central -portion of the visual cells with their contained nuclei, and the smaller, -proximal ends of the pigment cells. It would, therefore, give the reverse -appearance from the preceding section, namely, that of large unpigmented -(or but slightly pigmented) areas (the swollen bodies and nuclei -of the spindle-shaped cells), and in between them smaller pigmented -areas, the ends of the proximally tapering pigment cells (’89, Taf. II, Fig. -20). A section on the other side of the one first described, that is, one of -the first through the vitreous body, would show pigment areas of the -same size as the large ends of the pigment cells (the cone-shaped streaks -of pigment in the vitreous body which according to Schewiakoff are -associated with the pigment cell), and in between them the cross-sections -of the rod-like processes from the visual cells, lying in canals in the clear -homogeneous ground-substance of the vitreous body (’89, Taf. II, Fig. 18).</p> - -<p>Let me give a resumé of Schewiakoff’s conception of the structure -of the retina.</p> - -<p>a. There is an alternation of pigment and visual cells, the nuclei of -the spindle-shaped visual cells lying at a lower level than those of the -cone-shaped pigment cells.</p> - -<p>b. From the visual cells extend rod-like processes into the vitreous -body, lying in canals in the latter.</p> - -<p>c. In the vitreous body a cone-shaped streak of pigment overlies -each pigment cell of the retina, which is not a part of that cell.</p> - -<p>d. Apart from these pigment streaks and the rod-like processes of -the visual cells the vitreous body is structureless, probably a secretion of -the pigment cells.</p> - -<p>My own work, now, has led me to a different conception, so that my -conclusions on the same points would be as follows:</p> - -<p><span class="pagenum"><a name="Page_49" id="Page_49">[49]</a></span></p> - -<p>a. There is not good evidence of an alternation of cone-shaped pigment -cells and spindle-shaped visual cells, with the nuclei of the latter at -a lower level than those of the former.</p> - -<p>b. From some of the retinal cells otherwise not distinguished, there -extend rod-like processes into the vitreous body, such as described by -Schewiakoff.</p> - -<p>c. The cone-shaped streaks of pigment in the vitreous body belong -to the underlying pigment cells, in fact are direct continuations of them, -and at their distal ends they are prolonged into fibrous processes lying -in canals of the vitreous body exactly like the visual fibres of Schewiakoff.</p> - -<p>d. The vitreous body is not a homogeneous secretion, but is composed -of prisms of refracting substance, each with a denser central fibre.</p> - -<p>Let us go over these four points in detail.</p> - -<p>(a) As to the first, the question whether there is an alternation of -pigment and visual cells, I am not prepared as yet to make a positive -statement, since my not seeing both kinds as they are described has -little evidential value against the fact that Claus and Schewiakoff both -claim to have seen them. Perhaps proof could be obtained one way or -the other by maceration of fresh or of specially prepared material, -which none of us had. My evidence for not confirming alternation rests -wholly upon sections. <a href="#plate8">Fig. 58</a> represents a radial section through part -of the larger eye of Charybdea, made from an osmic preparation which -in this case showed two advantages over the material fixed in corrosive-acetic -(usually by all odds the best), namely, that the vitreous body (<i>vb</i>) -was not shrunken away from the retinal cells, as almost invariably -happens, and that the retinal cells were contracted apart from one -another in some places in such a way as to be almost equal to a macerated -preparation. Now, in the figure it is seen that there is an apparent -alternation of two kinds of cells, more regular than I usually find, but -the ones that are undoubtedly the pigment cells of Schewiakoff are the -ones that show the fibrous processes like his visual cells, and the pigment -streaks in the vitreous body are seen to be integral parts of the cells, not -cone-shaped masses lying in the vitreous body, merely associated with -the pigment cells. If these <em>are</em> the pigment cells of Schewiakoff, the -shorter cells in between must be his visual cells, yet they can by no -means be said to conform to a spindle-shaped type, nor are their nuclei -always at a lower level than (that is, internal to) those of the pigment -cells. If the long cells with the fibres are, on the other hand, considered<span class="pagenum"><a name="Page_50" id="Page_50">[50]</a></span> -the visual cells of Schewiakoff, then again we find nonconformity to a -spindle-shaped type, and nuclei not always at a lower level. The matter -of alternation of nuclei at different levels seems to me any way too slight -a distinction upon which to base a difference in function. It is a necessary -mechanical consequence of the crowding together of many cells on -one surface. And in many cases in perfectly radial sections through the -retina I find the nuclei fewer in number and arranged in very nearly a -single level. The retina of the smaller eye represented in <a href="#plate8">Fig. 69</a> shows -this. In sections further along in the same series the nuclei are found -at different levels, due without doubt to the slanting cut.</p> - -<div class="figcenter" style="width: 500px;" id="fig72"> - -<img src="images/figure.jpg" width="350" height="500" alt="" /> - -<p class="smaller">[Dr. Conant did not complete Fig. 72, and the accompanying outline of Fig. 7 of -Schewiakoff’s memoir (Beiträge zur Kenntnis des Acalephenauges, Morph. Jahrb., -Bd. XV, H. 1) has been substituted.—<span class="smcap">Editor.</span>]</p> - -<p class="smaller"><span class="smcap">Explanation of Letters in Text Figure.</span>—<i>C</i>—concretion cavity; <i>CO</i>—cornea; -<i>CP</i>—capsule of lens; <i>CSC</i>—cavity of sensory club; <i>EC</i>—ectoderm; <i>EN</i>—endoderm; -<i>ENC</i>—endoderm of sensory club; <i>L</i>—lens; <i>NC</i>—network cells; <i>NF</i>—nerve fibres; -<i>RT</i>—retina; <i>SLA</i>—supporting lamella; <i>VF</i>—vitreous body.</p> - -</div> - -<p><a href="#fig72">Fig. 72</a> is a horizontal section through the large eye, and shows that -here, too, when the sections pass through the eye just radially, the<span class="pagenum"><a name="Page_51" id="Page_51">[51]</a></span> -nuclei are not found at different levels sufficiently definite to suggest two -kinds of cells.</p> - -<p>In the inner corner of the retina in the same figure (<a href="#plate8">69</a>) are seen -cells without pigment which show nuclei undoubtedly at different levels. -These cells in this position are a regular feature in the retina of the -smaller eye. Schewiakoff considers them purely visual, because of the -lack of pigment. In so doing it seems to me he forgets his own standard -for discriminating between pigment and visual cells. The pigment cells -of the retina, according to him, are the same thing as the cone-shaped -supporting cells found elsewhere in the nervous epithelium, and are, -therefore, distinguished from the visual cells primarily by shape and by -position of nucleus, secondarily by the greater development of pigment. -When on the ground of pigmentation alone he calls the cells in the -corner of the retina visual, he judges them by only the second test, and -in so doing virtually admits, as it seems to me, that shape of cell and -position of nucleus are matters of no great moment. His own standards -place him in a dilemma. If on the other hand he judges by the lack of -pigment, the cells are visual; if by shape of cell and position of nucleus, -they are both visual and pigment cells without the pigment or supporting -cells. What use there would be for simple unpigmented cells in -one limited region of the retina is hard to see, so he naturally takes the -other horn of the dilemma and calls them visual because they have little -or no pigment.</p> - -<p>The distinction, then, between pigment and visual cells is brought -down to one of pigmentation only. Schewiakoff’s test for this is that in -the visual cells “Das Pigment durchsetzt aber nicht das ganze Protoplasma -des centralen Zellenabschnittes, sondern ist auf seine Oberfläche -beschrankt (Fig. 19, <i>sz</i>), so dass der innere, axiale, stark lichtbrechende -Theil vollkommen frei von demselben ist.” (’89, p. 37.) That is, in a -section through the ends of the retinal cells each pigment cell will -appear as a uniformly pigmented area, while each visual cell will appear -as a light, strongly refracting spot with a ring of pigment around its -periphery. This is the arrangement given in his Fig. 19.</p> - -<p>An arrangement so definite ought to be easily made out in sections, -yet I have not been able to find it so. My sections show considerable -difference in the amount of pigmentation even in material preserved -with the same killing agent. If the retina is heavily pigmented the -ends of the cells have the appearance shown in <a href="#plate8">Fig. 62</a>, which represents -a portion of a cross-section. The ends are seen as clearly defined<span class="pagenum"><a name="Page_52" id="Page_52">[52]</a></span> -polygonal areas differing among themselves in size, but not showing two -types of size, or two kinds of pigmentation, the one uniform, the other a -ring of pigment around a highly refracting central portion. If the -retina is but slightly pigmented—and some were so light as to make -depigmentation unnecessary—a difference is seen in the pigment, as -shown in <a href="#plate8">Fig. 63</a>, but in no case were areas found that showed a highly -refracting centre surrounded by a ring of pigment. (The unexplained -structures in <a href="#plate8">Fig. 63</a> will be referred to a little later.)</p> - -<p><a href="#plate8">Figures 59-62</a> are a series of four successive sections drawn with the -camera lucida for comparison with Schewiakoff’s Figs. 20 and 19, and -to show that the presence of two types of cells plainly marked within the -retina by the position of the nuclei at different levels is at least not clearly -demonstrated. Only the nuclei are drawn, since the cell bodies are not -easily distinguished from the surrounding fibres. The eye is the same as -that from which <a href="#fig72">Fig. 72</a> was made. <a href="#plate8">Fig. 59</a> shows a relatively small -number of nuclei of slightly larger size than usual. These I take for two -reasons to be nuclei of the ganglion cells that are found in the fibres at -the base of the retinal cells (Figs. <a href="#plate8">58</a>, <i>gc</i>, <a href="#plate8">69</a> and <a href="#fig72">72</a>). They are the first -nuclei struck in tracing sections toward the retina, and in the series from -which <a href="#plate8">Fig. 58</a> was taken similar nuclei appeared in both transverse and -radial cuts through the retina stained brightly and clearly with hæmatoxylin, -whereas the nuclei of the retinal cells proper were stained a -diffuse brownish-yellow from pigment that had evidently gone into -solution. <a href="#plate8">Fig. 60</a> shows the closely aggregated, smaller nuclei of the -retinal cells surrounded by the nuclei of the outlying ganglion cells. -Schewiakoff’s corresponding drawing (’89, Fig. 20) shows at this level a -definite alternation of the bodies and nuclei of unpigmented visual cells, -with the smaller, pigmented, proximal processes of the pigment cells. In -the next section (<a href="#plate8">Fig. 61</a>) the pigmented ends of a few of the cells have -been struck, and the following section (<a href="#plate8">Fig. 62</a>) shows that, in this -heavily pigmented specimen at least, there is no good evidence within -the retina itself of two kinds of cells, so that it is apparent that at any -rate we cannot accept Schewiakoff’s conception of the structure.</p> - -<p>(b) Yet the fibres that Schewiakoff observed and associated with -special visual cells occur beyond question. <a href="#plate8">Fig. 64</a> is a drawing of the -first cut through the vitreous body of Charybdea, and in among the -sections of the pigment streaks are seen sections of processes lying -within clear spaces exactly as Schewiakoff figures his visual fibres (’89, -Taf. II, Fig. 18). That the fibres occur is indisputable, but as to the cells<span class="pagenum"><a name="Page_53" id="Page_53">[53]</a></span> -to which they belong I can say nothing except that from such evidence -as I have given in the preceding paragraph I conclude that they come -from pigmented retinal cells of not very different type within the retina -from the others, if different at all.</p> - -<p>(c) On the third point, that the pigment streaks in the vitreous -body belong to underlying cells and are continued distally into fibrous -processes like the visual fibres of Schewiakoff, the evidence is decisive. -<a href="#plate8">Fig. 58</a> has already shown it, and if this were not enough, a case of -unusual stoutness of the fibres drawn in <a href="#plate8">Fig. 67</a> is conclusive. The -preparation from which the section is taken was one preserved with -corrosive-acetic, and I have drawn the outlines with the camera in order -to avoid exaggeration of the fibres as far as possible, and also to show -the shrinkage of the vitreous body (<i>vb</i>). It is the shrinkage of the -vitreous body that makes it so difficult to determine the exact relation of -structures seen in the vitreous body to the retina. The fibrous processes -run through the vitreous body to the “capsule” of the lens (<i>cp</i>) (see -also <a href="#fig72">Fig. 72</a>), a layer of homogeneous substance much resembling that of -the vitreous body, which is classed as a part of the vitreous body, but -usually in the shrinking adheres to the lens. The capsule is therefore -regarded by Schewiakoff as a secretion of the lens cells. Some fibres -were found by him to have the appearance of branching upon reaching -the surface of the capsule, others of passing through it and of seemingly -ending among the cells of the lens. The same appearances were given -in my sections. It is altogether impossible in the distal portion of the -vitreous body to distinguish between the fibres of Schewiakoff and those -that come from the long pigment cells. (<a href="#plate8">Figs. 64-66</a> represent the -appearance of the vitreous body at successive levels, and are from the -same series of sections as <a href="#plate8">Figs. 59-62</a> and <a href="#fig72">72</a>.) In Fig. 64 the sections of -the processes that Schewiakoff calls visual are easily distinguished from -the sections of the long pigment cells. In <a href="#plate8">Fig. 65</a>, which is two or three -sections nearer the lens, the pigment cells are shown by their cross-sections -to be tapering down, and in <a href="#plate8">Fig. 66</a>, nearer still to the lens, the -two kinds of processes are no longer to be distinguished from each other. -In a few cases I have found pigment in a fibre which but for this would -be called one of the visual fibres of Schewiakoff. Such considerations as -these, the similar appearance in cross-section, the finding of pigment in -a few cases, and the inability to trace to any readily distinguished special -type of retinal cell, make me wonder whether the visual fibres of -Schewiakoff are anything more than the distal processes of pigment<span class="pagenum"><a name="Page_54" id="Page_54">[54]</a></span> -cells, into which the pigment granules happened not to be produced at -the moment of fixation.</p> - -<p><a href="#plate8">Fig. 63</a>, however, where the retina was only slightly pigmented, -rather speaks against this view, for the number of darkly pigmented -areas seen here (which are shown beyond question by radial sections to -belong to the long pigment cells) is not great enough to account for the -number of both pigment areas and visual fibres of Schewiakoff seen in -such a section as <a href="#plate8">Fig. 64</a>. This would throw the visual fibres of -Schewiakoff back upon some of the slightly pigmented cells of <a href="#plate8">Fig. 63</a>, -otherwise not distinguished. I think the question cannot be settled -without the maceration of fresh material, and experiments upon eyes -killed in the light and in the dark.</p> - -<p>In such cases as that of <a href="#plate8">Fig. 63</a> it would seem conclusively shown -that the long pigment cells must belong to a different type from the -short, but as I have already said I can find no regularity in either their -shape or in the position of their nuclei. And on the other hand <a href="#plate8">Fig. 58</a> -shows that the reverse relation may obtain and the long cells be less -deeply pigmented on the edge of the retina than their shorter neighbors, -so that it looks as if all the short cells had to do was to project half their -pigment out into the vitreous body in order to become exactly like the -long ones. This they could do if, as is possibly the case, they are prolonged -into “visual fibres” of Schewiakoff that have escaped observation -and so do not appear in the drawing.</p> - -<p><a href="#plate8">Fig. 58</a> shows one more thing that is worthy of remark in passing. -In the preparation in which the vitreous body (at this point at any rate) -was not shrunken away from the retina, the fibre from each long -pigment cell does not lie in a clearly defined space or “canal,” such as is -usually described as a constant structure of the vitreous body. Very -likely these canals are formed only by shrinkage around the fibres, and -the irregular shape of the spaces around the three fibres in <a href="#plate8">Fig. 67</a> rather -bears out the same supposition.</p> - -<p>As to the structure of the vitreous body, apart from the fibres and -pigment streaks already mentioned, I find it to be made up of prisms -extending from retina to capsule of lens, each containing a central axis -or fibre. <a href="#plate8">Fig. 64</a> shows that the space around the pigment areas and -“visual fibres,” instead of being homogeneous, is wholly filled with the -polygonal cross-sections of these prisms. In Charybdea they are generally -more difficult to perceive than in my best material of Tripedalia -which was killed in acetic acid. In this the polygonal areas stood apart<span class="pagenum"><a name="Page_55" id="Page_55">[55]</a></span> -from each other more plainly. Curiously enough I have been unable to -demonstrate in Tripedalia the “visual fibres” of Schewiakoff. Here and -there were found spaces that at first sight reminded of them (<a href="#plate8">Fig. 69</a>, <i>sh</i>), -but they contained no central fibre, and were probably due to shrinkage. -The polygonal areas themselves, however, often contained a clear -spot in the centre, at one side of which would be found the cross-section -of the fibre, as is shown in many cases in <a href="#plate8">Fig. 68</a>. The clear spot is here -undoubtedly due to shrinkage of the gelatinous substance of the prism.</p> - -<p>I think that these prisms and fibres are the direct continuations of -retinal cells. In a section such as that drawn in <a href="#plate8">Fig. 63</a>, which takes -just the very tops of the cells of a slightly pigmented retina, in the -centre of the section just grazing the space that lies between the retina -and the shrunken vitreous body, most of the cells toward the middle -(where especially the extreme tips are taken) show in their centres a dot -exactly corresponding to the dots in the polygonal areas of the vitreous -body. In the exact middle of the section, where only the cell walls -appear, slightly indicated, a dot is seen in each case. The size and shape -of the ends of the cells correspond with those of the polygonal areas in -the vitreous body, and I do not doubt that the latter are continuations of -the former. The vitreous body, then, instead of being homogeneous, is -composed of the clear highly refracting outer ends of retinal cells. The -assumption lies near that these are the true visual rods, but of course it -is assumption only.</p> - -<p>To give a brief review, the points in which my conclusions differ -from those of Schewiakoff are as follows: I find (1) that the long pigment -streaks are parts of retinal cells continued into processes like his -visual rods; (2) that the vitreous body is composed of prisms with central -fibres proceeding from retinal cells; (3) that I am unable to get satisfactory -evidence of two types of cell distinguishable within the retina, and -at any rate find considerable evidence against the two types he distinguishes.</p> - -<p>These results are not wholly satisfactory, for they leave us with -three kinds of fibrous processes in the vitreous body which for the -present we are unable to trace to three, or even two distinguishable -types of cell in the retina. It would be more pleasing if we could -confirm Schewiakoff’s simple conception of the structure, with its one set -of visual rods in the vitreous body referable to a clearly marked type of -sensory cells in the retina, but I think the evidence that has been brought -up justifies the conclusion that in some respects he saw too much, in<span class="pagenum"><a name="Page_56" id="Page_56">[56]</a></span> -other respects too little. This is not to be wondered at, since his material, -to judge from a single statement, consisted of but twelve marginal -bodies, and, moreover, the work on Charybdea forms but one portion -of a paper that is excellent for the clearness of its descriptions and illustrations.</p> - -<p>Before leaving the subject I must mention that Wilson suggested -from his observations on Chiropsalmus that the vitreous body had a -prismatic structure, but he was probably mistaken when he thought he -found evidence of nuclei in it. Claus says that the retina is composed of -pigment and rod cells alternating, and Wilson agrees with him, but -under a sketch of a sense cell from the nerve he makes the express statement -“not very well preserved.” It seems very probable, therefore, that -he followed Claus’s interpretation rather than independent observations, -and Claus interpreted his results very much by analogy of what had been -found in other forms.</p> - -<p>The smaller complex eye which is represented in <a href="#plate8">Fig. 69</a> agrees in -structure very closely with the larger. The chief differences are that -sections do not show pigment extending into the vitreous body, that -there is no “capsule” to the lens, and that the lens seems to be supported -by a kind of stalk formed by a thickening of gelatine of the supporting -lamella (<i>sl</i>). The gelatinous thickening lies between the lens and an outgrowth -of endodermal cells (<i>en</i>) from the canal of the club. This -outgrowth is a constant feature, figured by Claus and Schewiakoff for -Charybdea, and by Wilson for Chiropsalmus, and found in Tripedalia -also. The regularity of its appearance in all three genera leads one to -suspect that it may have some significance not yet understood.</p> - -<p>Just above the smaller eye there lies a mass of cells of peculiar -structure (<a href="#plate8">Fig. 69</a>, <i>nc</i>). They are of a rounded polygonal contour, with a -comparatively small circular nucleus in the centre, and are found in -this region only. In and amongst them bundles of fibrous tissue are -found in the sections, which pass from the surface cells to the supporting -lamella. Claus describes the contents of these cells as coarsely granular -protoplasm and says they cannot be taken for ganglion cells. He is -inclined to believe that they play the part of a special supporting tissue. -Schewiakoff, on the other hand, is convinced that they are ganglion cells, -and finds processes passing out from them (’89, Taf. II, Fig. 22). I find, -however, that the cell contours are perfectly regular and clearly without -processes, and it is incomprehensible to me how, if his material was at all -well preserved, he could for a moment have taken them for the same<span class="pagenum"><a name="Page_57" id="Page_57">[57]</a></span> -thing as the big multipolar ganglion cells with large nucleus and -nucleolus which lie in about the same region and were correctly described -and figured by Claus but are not specially mentioned by Schewiakoff. I -cannot agree with Claus, however, that their contents are composed of -coarsely granular protoplasm. That which appears such by low magnification -shows itself under high powers to be a beautiful network with -thickenings at the nodes of the meshes, which is brought out very plainly -by a cytoplasmic stain such as Lyons blue. Around the nucleus is seen -a more or less well-defined clear zone. What the function of the cell is -remains as unknown to me as to Claus and Schewiakoff.</p> - -<p>There is left one more point in reference to the nervous system upon -which I wish to say a word. Claus and Schewiakoff both describe the -wall of the crystalline sac as structureless, formed by the bare supporting -lamella. The credit is due to H. V. Wilson of finding in Chiropsalmus -that it has a special lining of epithelial cells, which he figures as a continuous, -flattened layer. In both Charybdea and Tripedalia I find traces -of the same in nuclei here and there, but whether they are the remains -of a once continuous layer or not the sections do not show satisfactorily.</p> - -<p>This ends the account of what it seemed worth while to say at -present upon the nervous system. In concluding, the writer wishes to -express his thanks for the help afforded by Dr. Wilson’s notes, in particular -on the subject of the vascular lamellæ, and desires to make -especial acknowledgment of his indebtedness to Professor Brooks, whose -suggestions, based upon many years of experience with the Medusæ, -have been most welcome and helpful, and whose evidences of unfailing -kindliness, both in Jamaica at the time the material was obtained and in -Baltimore when it was being studied in the laboratory, take a most -honored part in the pleasant memories associated with the work.</p> - -<hr class="chap" /> - -<h2>LITERATURE REFERRED TO.</h2> - -<p><span class="smcap">Clarke, H. J.</span> ’78. Lucernariæ and their Allies. Washington: Smithsonian -Institution.</p> - -<p><span class="smcap">Claus, C.</span> ’78. Ueber Charybdea marsupialis. Arb. aus d. Zool. Inst. d. Univ. -Wien, Band II, Heft 2.</p> - -<p><span class="smcap">Doflein, F.</span> ’96. Die Eibildung bei Tubularia. Zeitsch. f. wiss. Zool., Bd. LXII, -Heft 1.</p> - -<p><span class="smcap">Haeckel, E.</span> ’79. Das System der Medusen. Jena.—’81. Challenger Report on -the Deep-sea Medusæ. Vol. IV.</p> - -<p><span class="pagenum"><a name="Page_58" id="Page_58">[58]</a></span></p> - -<p><span class="smcap">Hertwig, O.</span> and R. ’78. Das Nervensystem und die Sinnesorgane der Medusen. -Leipzig.</p> - -<p><span class="smcap">Hesse, R.</span> ’95. Ueber das Nervensystem und die Sinnesorgane von Rhizostoma -Cuvieri. Zeitschr. f. wiss. Zool., Bd. LX, Heft 3.</p> - -<p><span class="smcap">Müller, F.</span> ’59. Zwei neue Quallen von St. Catherina (Brasilien). Abhandlungen -der naturf. Gesellschaft zu Halle.</p> - -<p><span class="smcap">Schewiakoff, W.</span> ’89. Beiträge zur Kenntniss des Acalephenauges. Morph. -Jahrb., Bd. XV, Heft 1.</p> - -<p><span class="smcap">Wilson, H. V.</span> Unpublished notes.</p> - -<hr class="chap" /> - -<h2>TABLE OF REFERENCE LETTERS.</h2> - -<table summary="Reference letters and their meanings"> - <tr> - <td class="tdr"><i>afr</i></td> - <td class="center">=</td> - <td>adradial furrow.</td> - </tr> - <tr> - <td class="tdr"><i>afr´</i></td> - <td class="center">=</td> - <td>furrow in Tripedalia that separates perradial from interrad. regions in lower half of bell. (In Charybdea the same furrow is directly continuous with <i>afr</i>.)</td> - </tr> - <tr> - <td class="tdr"><i>ax</i></td> - <td class="center">=</td> - <td>axis of nerve.</td> - </tr> - <tr> - <td class="tdr"><i>c</i></td> - <td class="center">=</td> - <td>concretion.</td> - </tr> - <tr> - <td class="tdr"><i>cc</i></td> - <td class="center">=</td> - <td>canal underneath <i>ivl</i>, connecting the two adjacent marginal pockets.</td> - </tr> - <tr> - <td class="tdr"><i>ccl</i></td> - <td class="center">=</td> - <td>circular canal.</td> - </tr> - <tr> - <td class="tdr"><i>ci</i></td> - <td class="center">=</td> - <td>cilia.</td> - </tr> - <tr> - <td class="tdr"><i>cm</i></td> - <td class="center">=</td> - <td>circular muscle.</td> - </tr> - <tr> - <td class="tdr"><i>co</i></td> - <td class="center">=</td> - <td>cornea.</td> - </tr> - <tr> - <td class="tdr"><i>cp</i></td> - <td class="center">=</td> - <td>capsule of lens.</td> - </tr> - <tr> - <td class="tdr"><i>cs</i></td> - <td class="center">=</td> - <td>covering scale of niche.</td> - </tr> - <tr> - <td class="tdr"><i>csc</i></td> - <td class="center">=</td> - <td>canal of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>ct</i></td> - <td class="center">=</td> - <td>canal of tentacle.</td> - </tr> - <tr> - <td class="tdr"><i>ct´</i></td> - <td class="center">=</td> - <td>beginning of canals of lateral tentacles in Tripedalia.</td> - </tr> - <tr> - <td class="tdr"><i>ec</i></td> - <td class="center">=</td> - <td>ectoderm.</td> - </tr> - <tr> - <td class="tdr"><i>ece</i></td> - <td class="center">=</td> - <td>ectoderm of exumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>ecs</i></td> - <td class="center">=</td> - <td>ectoderm of subumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>ed</i></td> - <td class="center">=</td> - <td>distal paired eye.</td> - </tr> - <tr> - <td class="tdr"><i>el</i></td> - <td class="center">=</td> - <td>larger unpaired eye.</td> - </tr> - <tr> - <td class="tdr"><i>en</i></td> - <td class="center">=</td> - <td>endoderm.</td> - </tr> - <tr> - <td class="tdr"><i>enc</i></td> - <td class="center">=</td> - <td>endoderm of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>enf</i></td> - <td class="center">=</td> - <td>tract of nerve fibres underlying endoderm.</td> - </tr> - <tr> - <td class="tdr"><i>enfl</i></td> - <td class="center">=</td> - <td>endoderm of floor of stomach.</td> - </tr> - <tr> - <td class="tdr"><i>enp</i></td> - <td class="center">=</td> - <td>endoderm of stomach pockets.</td> - </tr> - <tr> - <td class="tdr"><i>enr</i></td> - <td class="center">=</td> - <td>endoderm of roof of stomach.</td> - </tr> - <tr> - <td class="tdr"><i>ens</i></td> - <td class="center">=</td> - <td>endoderm of stomach.</td> - </tr> - <tr> - <td class="tdr"><i>ep</i></td> - <td class="center">=</td> - <td>proximal paired eye.</td> - </tr> - <tr> - <td class="tdr"><i>es</i></td> - <td class="center">=</td> - <td>smaller unpaired eye.</td> - </tr> - <tr> - <td class="tdr"><i>fc</i></td> - <td class="center">=</td> - <td>funnel leading into canal of sensory clubs.</td> - </tr> - <tr> - <td class="tdr"><i>fp</i></td> - <td class="center">=</td> - <td>fibre from subepithelial plexus of subumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>fph</i></td> - <td class="center">=</td> - <td>filaments of phacellus.</td> - </tr> - <tr> - <td class="tdr"><i>frn</i></td> - <td class="center">=</td> - <td>frenulum.</td> - </tr> - <tr> - <td class="tdr"><i>ft</i></td> - <td class="center">=</td> - <td>funnel-shaped depression in ectoderm axial to base of tentacle.</td> - </tr> - <tr> - <td class="tdr"><span class="pagenum"><a name="Page_59" id="Page_59">[59]</a></span><i>g</i></td> - <td class="center">=</td> - <td>gelatine.</td> - </tr> - <tr> - <td class="tdr"><i>gc</i></td> - <td class="center">=</td> - <td>ganglion cell.</td> - </tr> - <tr> - <td class="tdr"><i>ge</i></td> - <td class="center">=</td> - <td>gelatine of exumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>go</i></td> - <td class="center">=</td> - <td>gastric ostium.</td> - </tr> - <tr> - <td class="tdr"><i>gs</i></td> - <td class="center">=</td> - <td>gelatine of subumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>hvl</i></td> - <td class="center">=</td> - <td>horizontal vascular lamella.</td> - </tr> - <tr> - <td class="tdr"><i>i</i></td> - <td class="center">=</td> - <td>interradius.</td> - </tr> - <tr> - <td class="tdr"><i>if</i></td> - <td class="center">=</td> - <td>interradial funnel of bell cavity.</td> - </tr> - <tr> - <td class="tdr"><i>ifr</i></td> - <td class="center">=</td> - <td>interradial furrow.</td> - </tr> - <tr> - <td class="tdr"><i>ivl</i></td> - <td class="center">=</td> - <td>interradial vascular lamella.</td> - </tr> - <tr> - <td class="tdr"><i>l</i></td> - <td class="center">=</td> - <td>lens.</td> - </tr> - <tr> - <td class="tdr"><i>lv</i></td> - <td class="center">=</td> - <td>lip of valve.</td> - </tr> - <tr> - <td class="tdr"><i>m</i></td> - <td class="center">=</td> - <td>bell margin.</td> - </tr> - <tr> - <td class="tdr"><i>mc</i></td> - <td class="center">=</td> - <td>mucous cell.</td> - </tr> - <tr> - <td class="tdr"><i>mep</i></td> - <td class="center">=</td> - <td>mesogonial pocket.</td> - </tr> - <tr> - <td class="tdr"><i>mo</i></td> - <td class="center">=</td> - <td>mouth.</td> - </tr> - <tr> - <td class="tdr"><i>mp</i></td> - <td class="center">=</td> - <td>marginal pocket.</td> - </tr> - <tr> - <td class="tdr"><i>mp´</i></td> - <td class="center">=</td> - <td>smaller marginal pockets, in Tripedalia.</td> - </tr> - <tr> - <td class="tdr"><i>mst</i></td> - <td class="center">=</td> - <td>muscle of stock of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>mt</i></td> - <td class="center">=</td> - <td>muscle at base of tentacle.</td> - </tr> - <tr> - <td class="tdr"><i>n</i></td> - <td class="center">=</td> - <td>nerve.</td> - </tr> - <tr> - <td class="tdr"><i>nc</i></td> - <td class="center">=</td> - <td>network cells, in sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>nf</i></td> - <td class="center">=</td> - <td>nerve fibres.</td> - </tr> - <tr> - <td class="tdr"><i>nm</i></td> - <td class="center">=</td> - <td>nematocyst.</td> - </tr> - <tr> - <td class="tdr"><i>nst</i></td> - <td class="center">=</td> - <td>nerve of stalk of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>osn</i></td> - <td class="center">=</td> - <td>outline of sensory niche.</td> - </tr> - <tr> - <td class="tdr"><i>p</i></td> - <td class="center">=</td> - <td>perradius.</td> - </tr> - <tr> - <td class="tdr"><i>pe</i></td> - <td class="center">=</td> - <td>pedalium.</td> - </tr> - <tr> - <td class="tdr"><i>ph</i></td> - <td class="center">=</td> - <td>phacellus.</td> - </tr> - <tr> - <td class="tdr"><i>pr</i></td> - <td class="center">=</td> - <td>proboscis.</td> - </tr> - <tr> - <td class="tdr"><i>r</i></td> - <td class="center">=</td> - <td>reproductive organ.</td> - </tr> - <tr> - <td class="tdr"><i>rc</i></td> - <td class="center">=</td> - <td>remains of concretion.</td> - </tr> - <tr> - <td class="tdr"><i>rcl</i></td> - <td class="center">=</td> - <td>radial canal.</td> - </tr> - <tr> - <td class="tdr"><i>rg</i></td> - <td class="center">=</td> - <td>radial ganglion.</td> - </tr> - <tr> - <td class="tdr"><i>rm</i></td> - <td class="center">=</td> - <td>radial muscle.</td> - </tr> - <tr> - <td class="tdr"><i>rn</i></td> - <td class="center">=</td> - <td>radial nerve.</td> - </tr> - <tr> - <td class="tdr"><i>rns</i></td> - <td class="center">=</td> - <td>root of nerve of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>rs?</i></td> - <td class="center">=</td> - <td>remains of stalk (?) of sensory organ.</td> - </tr> - <tr> - <td class="tdr"><i>rt</i></td> - <td class="center">=</td> - <td>retina.</td> - </tr> - <tr> - <td class="tdr"><i>s</i></td> - <td class="center">=</td> - <td>stomach.</td> - </tr> - <tr> - <td class="tdr"><i>sc</i></td> - <td class="center">=</td> - <td>bell cavity.</td> - </tr> - <tr> - <td class="tdr"><i>scl</i></td> - <td class="center">=</td> - <td>sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>scn</i></td> - <td class="center">=</td> - <td>supporting cell of nerve.</td> - </tr> - <tr> - <td class="tdr"><i>se</i></td> - <td class="center">=</td> - <td>sensory epithelium.</td> - </tr> - <tr> - <td class="tdr"><i>sh</i></td> - <td class="center">=</td> - <td>shrinkage space.</td> - </tr> - <tr> - <td class="tdr"><i>sl</i></td> - <td class="center">=</td> - <td>stalk of lens.</td> - </tr> - <tr> - <td class="tdr"><i>sla</i></td> - <td class="center">=</td> - <td>supporting lamella.</td> - </tr> - <tr> - <td class="tdr"><i>sn</i></td> - <td class="center">=</td> - <td>sensory niche.</td> - </tr> - <tr> - <td class="tdr"><i>so</i></td> - <td class="center">=</td> - <td>sensory organ in proboscis of Tripedalia.</td> - </tr> - <tr> - <td class="tdr"><i>sp</i></td> - <td class="center">=</td> - <td>stomach pocket.</td> - </tr> - <tr> - <td class="tdr"><i>sph</i></td> - <td class="center">=</td> - <td>stalk of phacellus.</td> - </tr> - <tr> - <td class="tdr"><i>ss</i></td> - <td class="center">=</td> - <td>stalk of sensory organ, in proboscis.</td> - </tr> - <tr> - <td class="tdr"><span class="pagenum"><a name="Page_60" id="Page_60">[60]</a></span><i>st</i></td> - <td class="center">=</td> - <td>stalk of sensory club.</td> - </tr> - <tr> - <td class="tdr"><i>su</i></td> - <td class="center">=</td> - <td>suspensorium.</td> - </tr> - <tr> - <td class="tdr"><i>sub</i></td> - <td class="center">=</td> - <td>subumbrella.</td> - </tr> - <tr> - <td class="tdr"><i>tl</i></td> - <td class="center">=</td> - <td>lateral tentacle.</td> - </tr> - <tr> - <td class="tdr"><i>tm</i></td> - <td class="center">=</td> - <td>median tentacle.</td> - </tr> - <tr> - <td class="tdr"><i>v</i></td> - <td class="center">=</td> - <td>velarium.</td> - </tr> - <tr> - <td class="tdr"><i>va</i></td> - <td class="center">=</td> - <td>vacuole.</td> - </tr> - <tr> - <td class="tdr"><i>vb</i></td> - <td class="center">=</td> - <td>vitreous body.</td> - </tr> - <tr> - <td class="tdr"><i>vc</i></td> - <td class="center">=</td> - <td>velar canals.</td> - </tr> - <tr> - <td class="tdr"><i>ve</i></td> - <td class="center">=</td> - <td>edge of velarium.</td> - </tr> - <tr> - <td class="tdr"><i>vfs</i></td> - <td class="center">=</td> - <td>visual fibres, according to Schewiakoff.</td> - </tr> - <tr> - <td class="tdr"><i>vg</i></td> - <td class="center">=</td> - <td>valve of gastric ostium.</td> - </tr> - <tr> - <td class="tdr"><i>vl</i></td> - <td class="center">=</td> - <td>vascular lamella.</td> - </tr> - <tr> - <td class="tdr"><i>vlc</i></td> - <td class="center">=</td> - <td>vascular lamella connecting <i>vls</i> with <i>vlm</i>.</td> - </tr> - <tr> - <td class="tdr"><i>vlm</i></td> - <td class="center">=</td> - <td>vascular lamella of margin.</td> - </tr> - <tr> - <td class="tdr"><i>vls</i></td> - <td class="center">=</td> - <td>vascular lamella of sensory niche.</td> - </tr> - <tr> - <td class="tdr"><i>vlst</i></td> - <td class="center">=</td> - <td>vascular lamella of sensory niche at base of stalk.</td> - </tr> - <tr> - <td class="tdr"><i>wc</i></td> - <td class="center">=</td> - <td>wandering cells.</td> - </tr> - <tr> - <td class="tdr"><i>w-x-y-z</i></td> - <td class="center">=</td> - <td>successive levels of Figs. 40-43 on Fig. 5.</td> - </tr> -</table> - -<hr class="chap" /> - -<h2>DESCRIPTION OF FIGURES.</h2> - -<p>Fig. 1. Charybdea Xaymacana, from one of the four interradial sides.</p> - -<p>Fig. 2. The same from above.</p> - -<p>Fig. 3. The same from below, the four tentacles cut off.</p> - -<p>Fig. 4. The same cut in halves vertically (or radially) through a perradius.</p> - -<p>Fig. 5. The same out in halves vertically (or radially) through an interradius.</p> - -<p>Figs. 6-16. Diagrams of horizontal (or transverse) sections through C. Xaymacana -at successive levels.</p> - -<p>Fig. 17. Tripedalia cystophora, from one of the four interradial sides.</p> - -<p>Fig. 18. The same from below.</p> - -<p>Fig. 19. The same cut in halves vertically through a perradius.</p> - -<p>Fig. 20. The same cut in halves vertically through interradius.</p> - -<p>Figs. 21-30. Diagrams of horizontal sections through T. cystophora at successive -levels.</p> - -<p>(The following are of Charybdea, except when specially stated otherwise.)</p> - -<p>Fig. 31. Horizontal section through the suspensorium.</p> - -<p>Fig. 32. Diagram of a gastric ostium seen from the stomach side.</p> - -<p>Fig. 33. Diagram of a vertical section through a gastric ostium.</p> - -<p>Fig. 34. Diagram of a horizontal section through a gastric ostium.</p> - -<p>Fig. 35. Diagram to illustrate the formation of the central and peripheral gastro-vascular -systems of a Hydromedusa (<i>a</i>, <i>b</i>, and <i>c</i>) and a Cubomedusa (<i>d</i>).</p> - -<p>Fig. 36. Vertical section through the upper part of the bell, adradial, to show -horizontal vascular lamella.</p> - -<p>Fig. 37. Vertical section through the perradius, to show vascular lamella of the -niche of the margin.</p> - -<p>Fig. 38. Vertical section a little to one side of the last, to show same structure.</p> - -<p>Fig. 39. Horizontal section through the upper part of the sensory niche, to show -vascular lamella of the niche.</p> - -<p>Figs. 40-43. Horizontal sections through the base of a pedalium at successive -levels, <i>w-x-y-z</i>, Fig. 5, to show marginal lamella.</p> - -<p><span class="pagenum"><a name="Page_61" id="Page_61">[61]</a></span></p> - -<p>Fig. 44. Diagram to show relations of sensory niche, of bell margin and -velarium in adult Tripedalia. The velarium represented as pendant.</p> - -<p>Fig. 45. To show the same structure in a young Tripedalia.</p> - -<p>Fig. 46. Horizontal section through the last just at the margin, to compare with -Fig. 29.</p> - -<p>Fig. 47. Cross-section through the nerve ring.</p> - -<p>Fig. 48. The structure of the nerve as seen by focusing at successive levels.</p> - -<p>Fig. 49. Diagram to show the relation of the nerve ring to the sensory club.</p> - -<p>Fig. 50. Horizontal section through the upper part of the sensory niche, to show -passage of nerve root through gelatine of subumbrella to stalk of sensory club.</p> - -<p>Fig. 51. Vertical section through base of stalk of sensory club, to show same -passage.</p> - -<p>Fig. 52. Similar section to last, but nearer to perradius, to show sub-endodermal -tract of nerve fibres.</p> - -<p>Fig. 53. Sensory organ in proboscis of Tripedalia, as seen from surface in living -animal.</p> - -<p>Figs. 54 and 55. Sections of same sensory organ.</p> - -<p>Fig. 56. Vertical section through one side of proboscis, to show sensory organ -attached to endoderm. (Tripedalia.)</p> - -<p>Fig. 57. Diagram of the outlines of sensory club seen from the side, by camera -lucida.</p> - -<p>Fig. 58. Part of retina of larger complex eye cut radially.</p> - -<p>Figs. 59-62. Four sections in direct sequence through retinal cells transversely, -larger eye.</p> - -<p>Fig. 63. Transverse section through the tips of cells of a slightly pigmented -retina, larger eye.</p> - -<p>Figs. 64-66. Three transverse sections through vitreous body at different levels. -All from same series, but not in direct sequence; larger eye.</p> - -<p>Fig. 67. Radial section through retina, to show fibres from the long pigment -cells; larger eye.</p> - -<p>Fig. 68. Transverse section through vitreous body of Tripedalia near retina.</p> - -<p>Fig. 69. Vertical section through smaller complex eye.</p> - -<p>Fig. 70. Wandering cells, Charybdea.</p> - -<p>Fig. 71. Floating mass, from stomach pocket of Tripedalia.</p> - -<p>Fig. 72. Horizontal section through larger complex eye. (See text figure, <a href="#Page_50">p. 50</a>.)</p> - -<div class="figcenter bbox" id="plate1"> - -<p class="caption">CUBOMEDUSÆ. PLATE I.</p> - -<a href="images/plate1.jpg"><img src="images/plate1-sm.jpg" width="100" height="130" -alt="Plate 1 depicts Figures 1, 2, 3, 17 and 18" /></a> - -<p class="caption">Gilman Drew, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate2"> - -<p class="caption">CUBOMEDUSÆ. PLATE II.</p> - -<a href="images/plate2.jpg"><img src="images/plate2-sm.jpg" width="100" height="130" -alt="Plate 2 depicts Figures 4, 5, 19 and 20" /></a> - -<p class="caption">Conant & Crew, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate3"> - -<p class="caption">CUBOMEDUSÆ. PLATE III.</p> - -<a href="images/plate3.jpg"><img src="images/plate3-sm.jpg" width="100" height="130" -alt="Plate 3 depicts Figures 6, 7, 8, 9, 10, 11, 12, 13, 56 and 57" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate4"> - -<p class="caption">CUBOMEDUSÆ. PLATE IV.</p> - -<a href="images/plate4.jpg"><img src="images/plate4-sm.jpg" width="100" height="130" -alt="Plate 4 depicts Figures 14, 15, 16, 36, 37, 38, 39, 53, 54, 55, 70 and 71" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate5"> - -<p class="caption">CUBOMEDUSÆ. PLATE V.</p> - -<a href="images/plate5.jpg"><img src="images/plate5-sm.jpg" width="100" height="130" -alt="Plate 5 depicts Figures 21, 22, 23, 24, 25, 26 and 27" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate6"> - -<p class="caption">CUBOMEDUSÆ. PLATE VI.</p> - -<a href="images/plate6.jpg"><img src="images/plate6-sm.jpg" width="100" height="130" -alt="Plate 6 depicts Figures 28, 29, 30, 40, 41, 42, 43, 44, 45 and 46" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate7"> - -<p class="caption">CUBOMEDUSÆ. PLATE VII.</p> - -<a href="images/plate7.jpg"><img src="images/plate7-sm.jpg" width="100" height="130" -alt="Plate 7 depicts Figures 31, 32, 33, 34, 47, 48, 49, 50, 51 and 52" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - -<div class="figcenter bbox" id="plate8"> - -<p class="caption">CUBOMEDUSÆ. PLATE VIII.</p> - -<a href="images/plate8.jpg"><img src="images/plate8-sm.jpg" width="100" height="130" -alt="Plate 8 depicts Figures 35a, 35b, 35c, 35d, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68 and 69" /></a> - -<p class="caption">F.S. Conant, del. Heliotype Co., Boston.</p> - -</div> - - - - - - - - -<pre> - - - - - -End of the Project Gutenberg EBook of The Cubomedusæ, by Franklin Story Conant - -*** END OF THIS PROJECT GUTENBERG EBOOK THE CUBOMEDUSÆ *** - -***** This file should be named 54241-h.htm or 54241-h.zip ***** -This and all associated files of various formats will be found in: - http://www.gutenberg.org/5/4/2/4/54241/ - -Produced by Donald Cummings, Bryan Ness and the Online -Distributed Proofreading Team at http://www.pgdp.net (This -file was produced from images generously made available -by The Internet Archive/American Libraries.) - - -Updated editions will replace the previous one--the old editions -will be renamed. - -Creating the works from public domain print editions means that no -one owns a United States copyright in these works, so the Foundation -(and you!) can copy and distribute it in the United States without -permission and without paying copyright royalties. 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