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diff --git a/8700-h/old/chap15.html b/8700-h/old/chap15.html new file mode 100644 index 0000000..d2633ef --- /dev/null +++ b/8700-h/old/chap15.html @@ -0,0 +1,1360 @@ +<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN"> +<!-- saved from url=(0036)http://../Haeckel/The Evolution of Man --> +<html> +<head> +<meta name="generator" content="HTML Tidy, see www.w3.org"> +<title>The Evolution of Man: Title</title> +<meta content="text/html; charset=iso-8859-1" http-equiv="Content-Type"> +<meta content="MSHTML 5.00.2919.6307" name="GENERATOR"> +<link rel="stylesheet" href="haeckel.css" type="text/css"> +</head> +<body> +<center>THE EVOLUTION OF MAN<br> +Volume I<br> +<br> +<hr noshade size="1" align="center" width="10%"> +<br> +C<font size="-2">HAPTER</font> XV<br> +<br> +<b>FŒTAL MEMBRANES AND CIRCULATION</b></center> + +<br> + + +<p class="one">Among the many interesting phenomena that we have +encountered in the course of human embryology, there is an especial +importance in the fact that the development of the human body +follows from the beginning just the same lines as that of the other +viviparous mammals. As a fact, all the embryonic peculiarities that +distinguish the mammals from other animals are found also in man; +even the ovum with its distinctive membrane (<i>zona pellucida,</i> +<a href="chap6.html#Fig. 14">Fig. 14</a>) shows the same +typical</p> + +<br> + + +<center> +<table class="capt" width="303" summary= +"Fig. 179. Human embryos from the second to the fifteenth week, seen from the left."> +<tr> +<td align="justify"> +<img src="images2/fig179.GIF" width="303" height="315" alt= +"Human embryos from the second to the fifteenth week, seen from the left."> +<br><br><a name="Fig. 179">Fig. 179</a>—<b>Human +embryos from the second to the fifteenth week,</b> seen from the +left, the curved back turned towards the right. (Mostly from <i> +Ecker.</i>) II of fourteen days. III of three weeks. IV of four +weeks. V of five weeks. VI of six weeks. VII of seven weeks. VIII +of eight weeks. XII of twelve weeks. XV of fifteen weeks.</td> +</tr> +</table> +</center> + +<br> +<br> +<hr> +<p class="page"><a name="page 157">[ 157 ]</a></p> + +<p> </p> + +<p class="one">structure in all mammals (apart from the older +oviparous monotremes). It has long since been deduced from the +structure of the developed man that his natural place in the animal +kingdom is among the mammals. Linné (1735) placed him in +this class with the apes, in one and the same order +(<i>primates</i>), in his <i>Systema Naturæ.</i> This +position is fully confirmed by comparative embryology. We see that +man entirely resembles the higher mammals, and most of all the +apes, in embryonic development as well as in anatomic structure. +And if we seek to understand this ontogenetic agreement in the +light of the biogenetic law, we find that it proves clearly and +necessarily the descent of man from a series of other mammals, and +proximately from the primates. The common origin of man and the +other mammals from a single ancient stem-form can no longer be +questioned; nor can the immediate blood-relationship of man and the +ape.</p> + +<p>The essential agreement in the whole bodily form and inner +structure is still visible in the embryo of man and the other +mammals at the late stage of development at which the mammal-body +can be recognised as such. But at a somewhat earlier stage, in +which the limbs, gill-arches, sense-organs, etc., are already +outlined, we cannot yet recognise the mammal embryos as such, or +distinguish them from those of birds and reptiles. When we consider +still earlier stages of development, we are unable to discover any +essential difference in bodily structure between the embryos of +these higher vertebrates and those of the lower, the amphibia and +fishes. If, in fine, we go back to the construction of the body out +of the four germinal layers, we are astonished to perceive that +these four layers are the same in all vertebrates, and everywhere +take a similar part in the building-up of the fundamental organs of +the body. If we inquire as to the origin of these four secondary +layers, we learn that they always arise in the same way from the +two primary layers; and the latter have the same significance in +all the metazoa (<i>i.e.,</i> all animals except the unicellulars). +Finally, we see that the cells which make up the primary germinal +layers owe their origin in every case to the repeated cleavage of a +single simple cell, the stem-cell or fertilised ovum.</p> + + +<table class="capt" width="251" align="left" summary= +"Fig. 180. Very young human embryo of the fourth week, one-fourth of an inch long."> +<tr> +<td><img src="images2/fig180.GIF" width="251" height="267" alt= +"Very young human embryo of the fourth week, one-fourth of an inch long."> +<a name="Fig. 180">Fig. +180</a>—<b>Very young human embryo of the fourth week,</b> +one-fourth of an inch long (taken from the womb of a suicide eight +hours after death). (From <i>Rabl.</i>) <i>n</i> nasal pits, <i> +a</i> eye, <i>u</i> lower jaw, <i>z</i> arch of hyoid bone, <i> +k<sub>3</sub></i> and <i>k<sub>4</sub></i> third and fourth +gill-arch, <i>h</i> heart; <i>s</i> primitive segments, <i>vg</i> +fore-limb (arm), <i>hg</i> hind-limb (leg), between the two the +ventral pedicle.</td> +</tr> +</table> + + +<p>It is impossible to lay too much stress on this remarkable +agreement in the chief embryonic features in man and the other +animals. We shall make use of it later on for our monophyletic +theory of descent—the hypothesis of a common descent of man +and all the metazoa from the gastræa. The first rudiments of +the principal parts of the body, especially the oldest organ, the +alimentary canal, are the same everywhere; they have always the +same extremely simple form. All the peculiarities that distinguish +the various groups of animals from each other only appear gradually +in the course of embryonic development; and the closer the relation +of the various groups, the later they are found. We may formulate +this phenomenon in a definite law, which may in a sense be regarded +as an appendix to our biogenetic law. This is the law of the +ontogenetic connection of related animal forms. It runs: The closer +the</p> + +<br> +<hr> +<p class="page"><a name="page 158">[ 158 ]</a></p> + +<p> </p> + +<p class="one">relation of two fully-developed animals in respect +of their whole bodily structure, and the nearer they are connected +in the classification of the animal kingdom, the longer do their +embryonic forms retain their identity, and the longer is it +impossible (or only possible on the ground of subordinate features) +to distinguish between their embryos. This law applies to all +animals whose embryonic development is, in the main, an hereditary +summary of their ancestral history, or in which the original form +of development has been faithfully preserved by heredity. When, on +the other hand, it has been altered by cenogenesis, or disturbance +of development, we find a limitation of the law, which increases in +proportion to the introduction of new features by adaptation (cf. +Chapter I, pp. 4–6). Thus the apparent exceptions to the law +can always be traced to cenogenesis.</p> + +<table class="capt" width="255" align="left" summary= +"Fig. 181. Human embryo of the middle of the fifth week, one-third of an inch long."> +<tr> +<td><img src="images2/fig181.GIF" width="255" height="255" alt= +"Human embryo of the middle of the fifth week, one-third of an inch long."> +<a name="Fig. 180">Fig. +181</a>—<b>Human embryo of the middle of the fifth week,</b> +one-third of an inch long. (From <i>Rabl.</i>) Letters as in Fig. +180, except <i>sk</i> curve of skull, <i>ok</i> upper jaw, <i> +hb</i> neck-indentation.</td> +</tr> +</table> + + +<p>When we apply to man this law of the ontogenetic connection of +related forms, and run rapidly over the earliest stages of human +development with an eye to it, we notice first of all the +structural identity of the ovum in man and the other mammals at the +very beginning (Figs. 1, 14). The human ovum possesses all the +distinctive features of the ovum of the viviparous mammals, +especially the characteristic formation of its membrane (<i>zona +pellucida</i>), which clearly distinguishes it from the ovum of all +other animals. When the human fœtus has attained the age of +fourteen days, it forms a round vesicle (or “embryonic +vesicle”) about a quarter of an inch in diameter. A thicker +part of its border forms a simple sole-shaped embryonic shield +one-twelfth of an inch long <a href="chap13.html#Fig. 133">(Fig. +133).</a> On its dorsal side we find in the middle line the +straight medullary furrow, bordered by the two parallel dorsal or +medullary swellings. Behind, it passes by the neurenteric canal +into the primitive gut or primitive groove. From this the folding +of the two cœlom-pouches proceeds in the same way as in the +other mammals (cf. Fig. 96, 97). In the middle of the sole-shaped +embryonic shield the first primitive segments immediately begin to +make their appearance. At this age the human embryo cannot be +distinguished from that of other mammals, such as the hare or +dog.</p> + +<p>A week later (or after the twenty-first day) the human embryo +has doubled its length; it is now about one-fifth of an inch long, +and, when seen from the side, shows the characteristic bend of the +back, the swelling of the head-end, the first outline of the three +higher sense-organs, and the rudiments of the gill-clefts, which +pierce the sides of the neck (Fig. 179, III). The allantois has +grown out of the gut behind. The embryo is already entirely +enclosed in the amnion, and is only connected in the middle of the +belly by the vitelline duct with the embryonic vesicle, which +changes into the yelk-sac. There are no extremities or limbs at +this stage, no trace of arms or legs. The head-end has been +strongly differentiated from the tail-end; and the first outlines +of the cerebral vesicles in front, and the heart below, under the +fore-arm, are already more or less clearly seen. There is as yet no +real face. Moreover, we seek in vain at this stage a special +character that may distinguish the human embryo from that of other +mammals.</p> + +<p>A week later (after the fourth week, on the twenty-eighth to +thirtieth day of development) the human embryo has</p> + +<br> +<hr> +<p class="page"><a name="page 159">[ 159 ]</a></p> + +<p> </p> + +<center> +<table class="capt" width="284" summary= +"Fig. 182. Median longitudinal section of the tail of a human embryo, two-thirds of an inch long."> +<tr> +<td align="justify"> +<img src="images2/fig182.GIF" width="284" height="308" alt= +"Median longitudinal section of the tail of a human embryo, two-thirds of an inch long."> +<br><br><a name="Fig. 182">Fig. 182</a>—<b>Median +longitudinal section of the tail of a human embryo,</b> two-thirds +of an inch long. (From <i>Ross Granville Harrison.</i>) <i>Med</i> +medullary tube, <i>Ca.fil</i> caudal filament, <i>ch</i> chorda, +<i>ao</i> caudal artery, <i>V.c.i</i> caudal vein, <i>an</i> anus, +<i>S.ug</i> sinus urogenitalis.</td> +</tr> +</table> +</center> + +<br> + + +<p class="one">reached a length of about one-third of an inch (Fig +179 IV). We can now clearly distinguish the head with its various +parts; inside it the five primitive cerebral vesicles (fore-brain, +middle-brain, intermediate-brain, hind-brain, and after-brain); +under the head the gill-arches, which divide the gill-clefts; at +the sides of the head the rudiments of the eyes, a couple of pits +in the outer skin, with a pair of corresponding simple vesicles +growing out of the lateral wall of the fore-brain (Figs. 180, 181 +<i>a</i>). Far behind the eyes, over the last gill-arches, we see a +vesicular rudiment of the auscultory organ. The rudimentary limbs +are now clearly outlined—four simple buds of the shape of +round plates, a pair of fore (<i>vg</i>) and a pair of hind legs +(<i>hg</i>), the former a little larger than the latter. The large +head bends over the trunk, almost at a right angle. The latter is +still connected in the middle of its ventral side with the +embryonic vesicle; but the embryo has still further severed itself +from it, so that it already hangs out as the yelk-sac. The hind +part of the body is also very much curved, so that the pointed +tail-end is directed towards the head. The head and face-part are +sunk entirely on the still open breast. The bend soon increases so +much that the tail almost touches the forehead (Fig. 179 V.; Fig. +181). We may then distinguish three or four special curves on the +round dorsal surface—namely, a skull-curve in the region of +the second cerebral vesicle, a neck-curve at the beginning of the +spinal cord, and a tail-curve at the fore-end. This pronounced +curve is only shared by man and</p> + +<br> +<hr> +<p class="page"><a name="page 160">[ 160 ]</a></p> + +<p> </p> + +<p class="one">the higher classes of vertebrates (the amniotes); it +is much slighter, or not found at all, in the lower vertebrates. At +this age (four weeks) man has a considerable tail, twice as long as +his legs. A vertical longitudinal section through the middle plane +of this tail (Fig. 182) shows that the hinder end of the spinal +marrow extends to the point of the tail, as also does the +underlying chorda (<i>ch</i>), the terminal continuation of the +vertebral column. Of the latter, the rudiments of the seven +coccygeal (or lowest) vertebræ are visible—thirty-two +indicates the third and thirty-six the seventh of these. Under the +vertebral column we see the hindmost ends of the two large +blood-vessels of the tail, the principal artery (<i>aorta +caudalis</i> or <i>arteria sacralis media, Ao</i>), and the +principal vein (<i>vena caudalis</i> or <i>sacralis media</i>). +Underneath is the opening of the anus (<i>an</i>) and the +urogenital sinus (<i>S.ug</i>). From this anatomic structure of the +human tail it is perfectly clear that it is the rudiment of an +ape-tail, the last hereditary relic of a long hairy tail, which has +been handed down from our tertiary primate ancestors to the present +day.</p> + +<br> + +<table class="capt" align="center" width="400" cellpadding="10" cellspacing="0" summary= +"Fig. 183. Human embryo, four weeks old, opened on the ventral side."> +<tr> +<td align="justify" width="186" valign="bottom"><img src="images2/fig183.GIF" width="186" height="308" alt= +"Human embryo, four weeks old, opened on the ventral side."> +<a name="Fig. 183">Fig. +183</a>—<b>Human embryo, four weeks old,</b> opened on the +ventral side. Ventral and dorsal walls are cut away, so as to show +the contents of the pectoral and abdominal cavities. All the +appendages are also removed (amnion, allantois, yelk-sac), and the +middle part of the gut. <i>n</i> eye, <i>3</i> nose, <i>4</i> upper +jaw, <i>5</i> lower jaw, <i>6</i> second, <i>6''</i> third +gill-arch, <i>ov</i> heart (<i>o</i> right, <i>o'</i> left auricle; +<i>v</i> right, <i>v'</i> left ventricle), <i>b</i> origin of the +aorta, <i>f</i> liver (<i>u</i> umbilical vein), <i>e</i> gut (with +vitelline artery, cut off at <i>a'</i>), <i>j'</i> vitelline vein, +<i>m</i> primitive kidneys, <i>t</i> rudimentary sexual glands, <i> +r</i> terminal gut (cut off at the mesentery <i>z</i>), <i>n</i> +umbilical artery, <i>u</i> umbilical vein, <i>9</i> fore-leg, <i> +9'</i> hind-leg. (From <i>Coste.</i>)</td> + +<td align="justify" valign="bottom" width="186"><img src="images2/fig184.GIF" width="186" height="387" alt= +"Human embryo, five weeks old, opened from the ventral side."> +<a name="Fig. 184">Fig. +184</a>—<b>Human embryo, five weeks old,</b> opened from the +ventral side (as in Fig. 183). Breast and belly-wall and liver are +removed. <i>3</i> outer nasal process, <i>4</i> upper jaw, <i>5</i> +lower jaw, <i>z</i> tongue, <i>v</i> right, <i>v'</i> left +ventricle of heart, <i>o'</i> left auricle, <i>b</i> origin of +aorta, <i>b', b'', b'''</i> first, second, and third aorta-arches, +<i>c, c', c''</i> vena cava, <i>ae</i> lungs (<i>y</i> pulmonary +artery), <i>e</i> stomach, <i>m</i> primitive kidneys (<i>j</i> +left vitelline vein, <i>s</i> cystic vein, <i>a</i> right vitelline +artery, <i>n</i> umbilical artery, <i>u</i> umbilical vein), <i> +x</i> vitelline duct, <i>i</i> rectum, <i>8</i> tail, <i>9</i> +fore-leg, <i>9'</i> hind-leg. (From <i>Coste.</i>)</td> +</tr> +</table> + + + +<p>It sometimes happens that we find even external relics of this +tail growing. According to the illustrated works of</p> + +<br> +<hr> +<p class="page"><a name="page 161">[ 161 ]</a></p> + +<p> </p> + +<p class="one">Surgeon-General Bernhard Ornstein, of Greece, these +tailed men are not uncommon; it is not impossible that they gave +rise to the ancient fables of the satyrs. A great number of such +cases are given by Max Bartels in his essay on “Tailed +Men” (1884, in the <i>Archiv für Anthropologie,</i> Band +XV), and critically examined. These atavistic human tails are often +mobile; sometimes they contain only muscles and fat, sometimes also +rudiments of caudal vertebræ. They have a length of eight to +ten inches and more. Granville Harrison has very carefully studied +one of these cases of “pigtail,” which he removed by +operation from a six months old child in 1901. The tail moved +briskly when the child cried or was excited, and was drawn up when +at rest.</p> + +<br> + +<table class="capt" align="center" width="300" cellpadding="10" cellspacing="0" summary="Fig. 185. The head of Miss Julia Pastrana."> +<tr> +<td align="center" valign="middle" width="150"><img src="images2/fig185.GIF" width="150" height="137" alt= +"The head of Miss Julia Pastrana."> +<a name="Fig. 185">Fig. +185</a>—<b>The head of Miss Julia Pastrana.</b> (From a +photograph by <i>Hintze.</i>)</td> + +<td align="justify" valign="top" width="150"><img src="images2/fig186.GIF" width="150" height="165" alt= +"Human ovum of twelve to thirteen days."> +<a name="Fig. 186">Fig. 186</a>—<b>Human ovum of twelve to thirteen days (?).</b> +(From <i>Allen Thomson.</i>) 1. Not opened. 2. Opened and +magnified. Within the outer chorion the tiny curved fœtus +lies on the large embryonic vesicle, to the left above.</td> +</tr> +</table> + + +<table class="capt" align="center" width="400" cellpadding="10" cellspacing="0" +summary="Fig. 187. Human ovum of ten days. Fig. 188. Human foetus of ten days, taken from the preceding ovum, magnified."> +<tr> +<td align="justify" width="192" valign="middle"><img src="images2/fig187.GIF" width="192" height="165" alt= +"Fig. 187. Human ovum of ten days. Fig. 188. Human foetus of ten days, taken from the preceding ovum, magnified."> +<a name="Fig. 187">Fig. +187</a>—<b>Human ovum of ten days.</b> (From <i>Allen +Thomson.</i>) Opened; the small fœtus in the right half, +above.<br> +<a name="Fig. 188">Fig. 188</a>—<b>Human fœtus of ten +days,</b> taken from the preceding ovum, magnified, <i>a</i> +yelk-sac, <i>b</i> neck (the medullary groove already closed), <i> +c</i> head (with open medullary groove), <i>d</i> hind part (with +open medullary groove), <i>e</i> a shred of the amnion.</td> +<td align="justify" width="192" valign="top"><img src="images2/fig189.GIF" width="192" height="292" alt= +"Fig. 189. Human ovum of twenty to twenty-two days. Fig. 190. Human foetus of twenty to twenty-two days, taken from the preceding ovum, magnified."> +<a name="Fig. 189">Fig. +189</a>—<b>Human ovum</b> of twenty to twenty-two days. (From +<i>Allen Thomson.</i>) Opened. The chorion forms a spacious +vesicle, to the inner wall of which the small fœtus (to the +right above) is attached by a short umbilical cord.<br> +<a name="Fig. 190">Fig. 190</a>—<b>Human fœtus</b> of +twenty to twenty-two days, taken from the preceding ovum, +magnified. <i>a</i> amnion, <i>b</i> yelk-sac, <i>c</i> lower-jaw +process of the first gill-arch, <i>d</i> upper-jaw process of same, +<i>e</i> second gill-arch (two smaller ones behind). Three +gill-clefts are clearly seen. <i>f</i> rudimentary fore-leg, <i> +g</i> auditory vesicle, <i>h</i> eye, <i>i</i> heart.</td> +</tr> +</table> + + + +<p>In the opinion of some travellers and anthropologists, the +atavistic tail-formation is hereditary in certain isolated tribes +(especially in south-eastern Asia and the archipelago), so that we +might speak of a special race or “species” of tailed +men</p> + +<br> +<hr> +<p class="page"><a name="page 162">[ 162 ]</a></p> + +<p> </p> + +<p class="one">(<i>Homo caudatus</i>). Bartels has “no doubt +that these tailed men will be discovered in the advance of our +geographical and ethnographical knowledge of the lands in +question” (<i>Archiv für Anthropologie,</i> Band XV, p. +129).</p> + +<center> +<table class="capt" width="371" summary= +"Fig. 191. Human embryo of sixteen to eighteen days."> +<tr> +<td align="justify"> +<img src="images2/fig191.GIF" width="371" height="384" alt= +"Human embryo of sixteen to eighteen days."> +<br><a name="Fig. 191">Fig. 191</a>—<b>Human +embryo of sixteen to eighteen days.</b> (From <i>Coste.</i>) +Magnified. The embryo is surrounded by the amnion, (<i>a</i>), and +lies free with this in the opened embryonic vesicle. The belly is +drawn up by the large yelk-sac (<i>d</i>), and fastened to the +inner wall of the embryonic membrane by the short and thick pedicle +(<i>b</i>). Hence the normal convex curve of the back (Fig. 190) is +here changed into an abnormal concave surface. <i>h</i> heart, <i> +m</i> parietal mesoderm. The spots on the outer wall of the +serolemma are the roots of the branching chorion-villi, which are +free at the border.</td> +</tr> +</table> +</center> + +<br> + + +<p>When we open a human embryo of one month <a href="#Fig. 183"> +(Fig. 183),</a> we find the alimentary canal formed in the +body-cavity, and for the most part cut off from the embryonic +vesicle. There are both mouth and anus apertures. But the +mouth-cavity is not yet separated from the nasal cavity, and the +face not yet shaped. The heart shows all its four sections; it is +very large, and almost fills the whole of the pectoral cavity (Fig. +183 <i>ov</i>). Behind it are the very small rudimentary lungs. The +primitive kidneys (<i>m</i>) are very large; they fill the greater +part of the abdominal cavity, and extend from the liver (<i>f</i>) +to the pelvic gut. Thus at the end of the first month all the chief +organs are already outlined. But there are at this stage no +features by which the human embryo materially differs from that of +the dog, the hare, the ox, or the horse—in a word, of any +other higher mammal. All these embryos have the same, or at least a +very similar, form; they can at the most be</p> + +<br> +<hr> +<p class="page"><a name="page 163">[ 163 ]</a></p> + +<p> </p> + +<p class="one">distinguished from the human embryo by the total +size of the body or some other insignificant difference in size. +Thus, for instance, in man the head is larger in proportion to the +trunk than in the ox. The tail is rather longer in the dog than in +man. These are all negligible differences. On the other hand, the +whole internal organisation and the form and arrangement of the +various organs are essentially the same in the human embryo of four +weeks as in the embryos of the other mammals at corresponding +stages.</p> + +<br> + + +<center> +<table class="capt" width="367" summary= +"Fig. 192. Human embryo of the fourth week, one-third of an inch long, lying in the dissected chorion."> +<tr> +<td align="center"> +<img src="images2/fig192.GIF" width="367" height="238" alt= +"Human embryo of the fourth week, one-third of an inch long, lying in the dissected chorion."> +<a name="Fig. 192">Fig. 192</a>—<b>Human +embryo</b> of the fourth week, one-third of an inch long, lying in +the dissected chorion.</td> +</tr> +</table> +</center> + +<br> + +<table class="capt" width="219" align="left" summary= +"Fig. 193. Human embryo of the fourth week, with its membranes, like Fig. 192, but a little older."> +<tr> +<td><img src="images2/fig193.GIF" width="219" height="239" alt= +"Human embryo of the fourth week, with its membranes, like Fig. 192, but a little older."> +<a name="Fig. 193">Fig. +193</a>—<b>Human embryo</b> of the fourth week, with its +membranes, like Fig. 192, but a little older. The yelk-sac is +rather smaller, the amnion and chorion larger.</td> +</tr> +</table> + +<p>It is otherwise in the second month of human development. <a +href="#Fig. 179">Fig. 179</a> represents a human embryo of six +weeks (VI), one of seven weeks (VII), and one of eight weeks +(VIII), at natural size. The differences which mark off the human +embryo from that of the dog and the lower mammals now begin to be +more pronounced. We can see important differences at the sixth, and +still more at the eighth week, especially in the formation of the +head. The size of the various sections of the brain is greater in +man, and the tail is shorter.</p> +<p> +Other differences between man and the +lower mammals are found in the relative size of the internal +organs. But even at this stage the human embryo differs very little +from that of the nearest related mammals—the apes, especially +the anthropomorphic apes.</p> + + +<p>The features by means of which we distinguish between them are +not clear until later on. Even at a much more advanced stage of +development, when we can distinguish the human fœtus from +that of the ungulates at a glance, it still closely resembles that +of the higher apes. At last we get the distinctive features, +and</p> + +<br> +<hr> +<p class="page"><a name="page 164">[ 164 ]</a></p> + +<p> </p> + +<p class="one">we can distinguish the human embryo confidently at +the first glance from that of all other mammals during the last +four months of fœtal life—from the sixth to the ninth +month of pregnancy. Then we begin to find also the differences +between the various races of men, especially in regard to the +formation of the skull and the face. (Cf. Chapter XXIII.)</p> + +<br> + + +<table class="capt" summary= +"Fig. 194. Human embryo with its membranes, six weeks old."> +<tr> +<td><img src="images2/fig194.GIF" width="270" height="238" alt= +"Human embryo with its membranes, six weeks old."></td> +<td align="left" valign="bottom"><a name="Fig. 194">Fig. +194</a>—<b>Human embryo with its membranes,</b> six weeks +old. The outer envelope of the whole ovum is the chorion, thickly +covered with its branching villi, a product of the serous membrane. +The embryo is enclosed in the delicate amnion-sac. The yelk-sac is +reduced to a small pear-shaped umbilical vesicle; its thin pedicle, +the long vitelline duct, is enclosed in the umbilical cord. In the +latter, behind the vitelline duct, is the much shorter pedicle of +the allantois, the inner lamina of which (the gut-gland layer) +forms a large vesicle in most of the mammals, while the outer +lamina is attached to the inner wall of the outer embryonic coat, +and forms the placenta there. (Half diagrammatic.)"></td> +</tr> +</table> + +<br> + + +<p>The striking resemblance that persists so long between the +embryo of man and of the higher apes disappears much earlier in the +lower apes. It naturally remains longest in the large +anthropomorphic apes (gorilla, chimpanzee, orang, and gibbon). The +physiognomic similarity of these animals, which we find so great in +their earlier years, lessens with the increase of age. On the other +hand, it remains throughout life in the remarkable long-nosed ape +of Borneo (<i>Nasalis larvatus</i>). Its finely-shaped nose would +be regarded with envy by many a man who has too little of that +organ. If we compare the face of the long-nosed ape with that of +abnormally ape-like human beings (such as the famous Miss Julia +Pastrana, Fig. 185), it will be admitted to represent a higher +stage of development. There are still people among us who look +especially to the face for the “image of God in man.” +The long-nosed ape would have more claim to this than some of the +stumpy-nosed human individuals one meets.</p> + +<p>This progressive divergence of the human from the animal form, +which is based on the law of the ontogenetic connection between +related forms, is found in the structure of the internal organs as +well as in external form. It is also expressed in the construction +of the envelopes and appendages that we find surrounding the +fœtus externally, and that we will now consider more closely. +Two of these appendages—the amnion and the +allantois—are only found in the three higher classes of +vertebrates, while the third, the yelk-sac, is found in most of the +vertebrates. This is a circumstance of great importance, and it +gives us valuable data for constructing man’s genealogical +tree.</p> + +<p>As regards the external membrane that encloses the ovum in the +mammal womb,</p> + +<br> +<hr> +<p class="page"><a name="page 165">[ 165 ]</a></p> + +<p> </p> + +<p class="one">we find it just the same in man as in the higher +mammals. The ovum is, the reader will remember, first surrounded by +the transparent structureless <i>ovolemma</i> or <i>zona +pellucida</i> (Figs. 1, 14). But very soon, even in the first week +of development, this is replaced by the permanent chorion. This is +formed from the external layer of the amnion, the <i>serolemma,</i> +or “serous membrane,” the formation of which we shall +consider presently; it surrounds the fœtus and its appendages +as a broad, completely closed sac; the space between the two, +filled with clear watery fluid, is the <i>serocœlom,</i> or +interamniotic cavity (“extra-embryonic body-cavity”). +But the smooth surface of the sac is quickly covered with numbers +of tiny tufts, which are really hollow outgrowths like the fingers +of a glove (Figs. 186, 191, 198 <i>chz</i>). They ramify and push +into the corresponding depressions that are formed by the tubular +glands of the mucous membrane of the maternal womb. Thus, the ovum +secures its permanent seat (Fig. 186–194).</p> + + +<table class="capt" width="232" align="left" summary= +"Fig. 195. Diagram of the embryonic organs of the mammal (foetal membranes and appendages)."> +<tr> +<td><img src="images2/fig195.GIF" width="232" height="228" alt= +"Diagram of the embryonic organs of the mammal (foetal membranes and appendages)."> +<a name="Fig. 195">Fig. +195</a>—<b>Diagram of the embryonic organs of the mammal</b> +(fœtal membranes and appendages). (From <i>Turner.</i>) <i>E, +M, H</i> outer, middle, and inner germ layer of the embryonic +shield, which is figured in median longitudinal section, seen from +the left. <i>am</i> amnion. <i>AC</i> amniotic cavity, <i>UV</i> +yelk-sac or umbilical vesicle, <i>ALC</i> allantois, <i>al</i> +pericœlom or serocœlom (inter-amniotic cavity), <i> +sz</i> serolemma (or serous membrane), <i>pc</i> prochorion (with +villi).)</td> +</tr> +</table> + +<p>In human ova of eight to twelve days this external membrane, the +chorion, is already covered with small tufts or villi, and forms a +ball or spheroid of one-fourth to one-third of an inch in diameter +(Figs. 186–188). As a large quantity of fluid gathers inside +it, the chorion expands more and more, so that the embryo only +occupies a small part of the space within the vesicle. The villi of +the chorion grow larger and more numerous. They branch out more and +more. At first the villi cover the whole surface, but they +afterwards disappear from the greater part of it; they then develop +with proportionately greater vigour at a spot where the placenta is +formed from the allantois.</p> + +<p>When we open the chorion of a human embryo of three weeks, we +find on the ventral side of the fœtus a large round sac, +filled with fluid. This is the yelk-sac, or “umbilical +vesicle,” the origin of which we have considered previously. +The larger the embryo becomes the smaller we find the yelk-sac. In +the end we find the remainder of it in the shape of a small +pear-shaped vesicle, fastened to a long thin stalk (or pedicle), +and hanging from the open belly of the fœtus <a href= +"#Fig. 194">(Fig. 194).</a> This pedicle is the vitelline duct, and +is separated from the body at the closing of the navel.</p> + +<p>Behind the yelk-sac a second appendage,</p> + +<br> +<hr> +<p class="page"><a name="page 166">[ 166 ]</a></p> + +<p> </p> + +<p class="one">of much greater importance, is formed at an early +stage at the belly of the mammal embryo. This is the allantois or +“primitive urinary sac,” an important embryonic organ, +only found in the three higher classes of vertebrates. In all the +amniotes the allantois quickly appears at the hinder end of the +alimentary canal, growing out of the cavity of the pelvic gut <a +href="chap13.html#Fig. 147">(Fig. 147 <i>r, u,</i></a> Fig. 195 <i> +ALC</i>).</p> + +<p>The further development of the allantois varies considerably in +the three sub-classes of the mammals. The two lower sub-classes, +monotremes and marsupials, retain the simpler structure of their +ancestors, the reptiles. The wall of the allantois and the +enveloping serolemma remains smooth and without villi, as in the +birds. But in the third sub-class of the mammals the serolemma +forms, by invagination at its outer surface, a number of hollow +tufts or villi, from which it takes the name of the <i>chorion</i> +or <i>mallochorion.</i> The gut-fibre layer of the allantois, +richly supplied with branches of the umbilical vessel, presses into +these tufts of the primary chorion, and forms the “secondary +chorion.” Its embryonic blood-vessels are closely correlated +to the contiguous maternal blood-vessels of the environing womb, +and thus is formed the important nutritive apparatus of the embryo +which we call the placenta.</p> + + +<table class="capt" width="217" align="left" summary= +"Fig. 196. Diagrammatic frontal section of the pregnant human womb."> +<tr> +<td><img src="images2/fig196.GIF" width="217" height="198" alt= +"Diagrammatic frontal section of the pregnant human womb."> +<a name="Fig. 196">Fig. +196</a>—<b>Diagrammatic frontal section of the pregnant human +womb.</b> (From <i>Longet.</i>) The embryo hangs by the umbilical +cord, which encloses the pedicle of the allantois (<i>al</i>). <i> +nb</i> umbilical vessel, <i>am</i> amnion, <i>ch</i> chorion, <i> +ds</i> decidua serotina, <i>dv</i> decidua vera, <i>dr</i> decidua +reflexa, <i>z</i> villi of the placenta, <i>c</i> cervix uteri, <i> +u</i> uterus.)</td> +</tr> +</table> + + +<p>The pedicle of the allantois, which connects the embryo with the +placenta and conducts the strong umbilical vessels from the former +to the latter, is covered by the amnion, and, with this amniotic +sheath and the pedicle of the yelk-sac, forms what is called the +<i>umbilical cord</i> (Fig. 196 <i>al</i>). As the large and +blood-filled vascular network of the fœtal allantois attaches +itself closely to the mucous lining of the maternal womb, and the +partition between the blood-vessels of mother and child becomes +much thinner, we get that remarkable nutritive apparatus of the +fœtal body which is characteristic of the placentalia (or +choriata). We shall return afterwards to the closer consideration +of this (cf. Chapter XXIII).</p> + +<p>In the various orders of mammals the placenta undergoes many +modifications, and these are in part of great evolutionary +importance and useful in classification. There is only one of these +that need be specially mentioned—the important fact, +established by Selenka in 1890, that the distinctive human +placentation is confined to the anthropoids. In this most advanced +group of the mammals the allantois is very small, soon loses its +cavity, and then, in common with the amnion, undergoes certain +peculiar changes. The umbilical cord develops in this case from +what is called the “ventral pedicle.” Until very +recently this was regarded as a structure peculiar to man. We now +know from Selenka that the much-discussed ventral pedicle is merely +the pedicle of the allantois, combined with the pedicle of the +amnion and the rudimentary pedicle of the yelk-sac. It has just the +same structure in the orang and gibbon (Fig. 197) and very probably +in the chimpanzee and gorilla, as in man; it is, therefore, not a +<i>disproof,</i> but a striking fresh proof, of the +blood-relationship of man and the anthropoid apes.</p> + +<p>We find only in the anthropoid apes—the gibbon and orang +of Asia and the chimpanzee and gorilla of Africa—the peculiar +and elaborate formation of the placenta that characterises man +(Fig. 198).</p> + +<br> +<hr> +<p class="page"><a name="page 167">[ 167 ]</a></p> + +<p> </p> + +<p class="one">In this case there is at an early stage an intimate +blending of the chorion of the embryo and the part of the mucous +lining of the womb to which it attaches. The villi of the chorion +with the blood-vessels they contain grow so completely into the +tissue of the uterus, which is rich in blood, that it becomes +impossible to separate them, and they form together a sort of cake. +This comes away as the “afterbirth” at parturition; at +the same time, the part of the mucous lining of the womb that has +united inseparably with the chorion is torn away; hence it is +called the <i>decidua</i> (“falling-away membrane”), +and also the “sieve-membrane,” because it is perforated +like a sieve. We find a decidua of this kind in most of the higher +placentals; but it is only in man and the anthropoid apes that it +divides into three parts—the outer, inner, and placental +decidua. The external or true decidua (Fig. 196 <i>du,</i> Fig. 199 +<i>g</i>) is the part of the mucous lining of the womb that clothes +the inner surface of the uterine cavity wherever it is not +connected with the placenta. The placental or spongy decidua +(<i>placentalis</i> or <i>serotina,</i> Fig. 196 <i>ds,</i> Fig. +199 <i>d</i>) is really the placenta itself, or the maternal part +of it (<i>placenta uterina</i>)—namely, that part of the +mucous lining of the womb which unites intimately with the +chorion-villi of the fœtal placenta. The internal or false +decidua (<i>interna</i> or <i>reflexa,</i> Fig. 196 <i>dr,</i> Fig. +199 <i>f</i>) is that part of the mucous lining of the womb which +encloses the remaining surface of the ovum, the smooth chorion +(<i>chorion læve</i>), in the shape of a special thin +membrane. The origin of these three different deciduous membranes, +in regard to which quite erroneous views (still retained in their +names) formerly prevailed, is now quite clear, The external <i> +decidua vera</i> is the specially modified and subsequently +detachable superficial stratum of the original mucous lining of the +womb. The placental <i>decidua serotina</i> is that part of the +preceding which is completely transformed by the ingrowth of the +chorion-villi, and is used for constructing the placenta. The inner +<i>decidua reflexa</i> is formed by the rise of a circular fold of +the mucous lining (at the border of the <i>decidua vera</i> and <i> +serotina</i>), which grows over the fœtus (like the anmnion) +to the end.</p> + +<br> + + +<center> +<table class="capt" width="381" summary= +"Fig. 197. Male embryo of the Siamang-gibbon (Hylobates siamanga) of Sumatra."> +<tr> +<td align="justify"> +<img src="images2/fig197.GIF" width="381" height="253" alt= +"Male embryo of the Siamang-gibbon (Hylobates siamanga) of Sumatra."> +<br><br><a name="Fig. 197">Fig. 197</a>—<b>Male +embryo of the Siamang-gibbon</b> (<i>Hylobates siamanga</i>) of +Sumatra; to the left the dissected uterus, of which only the dorsal +half is given. The embryo has been taken out, and the limbs folded +together; it is still connected by the umbilical cord with the +centre of the circular placenta which is attached to the inside of +the womb. This embryo takes the head-position in the womb, and this +is normal in man also.</td> +</tr> +</table> +</center> + +<br> + + +<p>The peculiar anatomic features that characterise the human +fœtal membranes are found in just the same way in the +higher</p> + +<br> +<hr> +<p class="page"><a name="page 168">[ 168 ]</a></p> + +<p> </p> + +<p class="one">apes. Until recently it was thought that the human +embryo was distinguished by its peculiar construction of a solid +allantois and a special ventral pedicle, and that the umbilical +cord developed from this in a different way than in the other +mammals. The opponents of the unwelcome “ape-theory” +laid great stress on this, and thought they had at last discovered +an important indication that separated man from all the other +placentals. But the remarkable discoveries published by the +distinguished zoologist Selenka in 1890 proved that man shares +these peculiarities of placentation with the anthropoid apes, +though they are not found in the other apes. Thus the very feature +which was advanced by our critics as a disproof became a most +important piece of evidence in favour of our pithecoid origin.)</p> + +<br> + + +<center> +<table class="capt" width="395" summary= +"Fig. 198. Frontal section of the pregnant human womb."> +<tr> +<td align="justify"> +<img src="images2/fig198.GIF" width="395" height="347" alt= +"Frontal section of the pregnant human womb."> +<br><a name="Fig. 198">Fig. +198</a>—<b>Frontal section of the pregnant human womb.</b> +(From <i>Turner.</i>) The embryo (a month old) hangs in the middle +of the amniotic cavity by the ventral pedicle or umbilical cord, +which connects it with the placenta (above).</td> +</tr> +</table> +</center> + +<br> + + +<p>Of the three vesicular appendages of the amniote embryo which we +have now described the amnion has no blood-vessels at any moment of +its existence. But the other two vesicles, the yelk-sac and the +allantois, are equipped with large blood-vessels, and these effect +the nourishment of the embryonic body. We may take the opportunity +to make a few general observations on the first circulation in the +embryo and its central organ, the heart. The first blood-vessels, +the heart, and the first blood itself, are formed from the +gut-fibre layer. Hence it was called by earlier embryologists the +“vascular layer.” In a sense the term is quite correct. +But it must not be understood as if all the blood-vessels in the +body came from this layer, or as if the whole of this layer were +taken up only with the formation of blood-vessels. Neither of these +suppositions is true. Blood-vessels may be formed independently in +other parts, especially in the various products of the skin-fibre +layer.</p> + +<br> +<hr> +<p class="page"><a name="page 169">[ 169 ]</a></p> + +<p> </p> + +<center> +<table class="capt" width="241" summary= +"Fig. 199. Human foetus, twelve weeks old, with its membranes."> +<tr> +<td align="justify"> +<img src="images2/fig199.GIF" width="241" height="276" alt= +"Human foetus, twelve weeks old, with its membranes."> +<br><a name="Fig. 199">Fig. 199</a>—<b>Human +fœtus, twelve weeks old, with its membranes.</b> The +umbilical cord goes from its navel to the placenta. <i>b</i> +amnion, <i>c</i> chorion, <i>d</i> placenta, <i>d</i> apostrophe, +relics of villi on smooth chorion, <i>f</i> internal or reflex +decidua, <i>g</i> external or true decidua. (From <i>B. +Schultze.</i>)</td> +</tr> +</table> + +<br> +<table class="capt" width="281" summary= +"Fig. 200. Mature human foetus (at the end of the pregnancy, in its natural position, taken out of the uterine cavity)."> +<tr> +<td align="justify"> +<img src="images2/fig200.GIF" width="281" height="195" alt= +"Mature human foetus (at the end of the pregnancy, in its natural position, taken out of the uterine cavity)."> +<br><a name="Fig. 200">Fig. 200</a>—<b>Mature +human fœtus</b> (at the end of pregnancy, in its natural +position, taken out of the uterine cavity). On the inner surface of +the latter (to the left) is the placenta, which is connected by the +umbilical cord with the child’s navel. (From <i>Bernhard +Schultze.</i>)</td> +</tr> +</table> +</center> + +<br> +<hr> +<p class="page"><a name="page 170">[ 170 ]</a></p> + +<p> </p> + +<p>The first blood-vessels of the mammal embryo have been +considered by us previously, and we shall study the development of +the heart in the second volume.</p> + +<p>In every vertebrate it lies at first in the ventral wall of the +fore-gut, or in the ventral (or cardiac) mesentery, by which it is +connected for a time with the wall of the body. But it soon severs +itself from the place of its origin, and lies freely in a +cavity—the cardiac cavity. For a short time it is still +connected with the former by the thin plate of the mesocardium. +Afterwards it lies quite free in the cardiac cavity, and is only +directly connected with the gut-wall by the vessels which issue +from it.</p> + +<br> + + +<center> +<table class="capt" width="288" summary= +"Fig. 201. Vitelline vessels in the germinative area of a chick-embryo, at the close of the third day of incubation."> +<tr> +<td align="justify"> +<img src="images2/fig201.GIF" width="288" height="283" alt= +"Vitelline vessels in the germinative area of a chick-embryo, at the close of the third day of incubation."> +<br><br><a name="Fig. 201">Fig. +201</a>—<b>Vitelline vessels in the germinative area of a +chick-embryo,</b> at the close of the third day of incubation. +(From <i>Balfour.</i>) The detached germinative area is seen from +the ventral side: the arteries are dark, the veins light. <i>H</i> +heart, <i>AA</i> aorta-arches, <i>Ao</i> aorta, <i>R.of.A</i> right +omphalo-mesenteric artery, <i>S.T.</i> sinus terminalis, <i> +L.Of</i> and <i>R.Of</i> right and left omphalo-mesenteric veins, +<i>S.V.</i> sinus venosus, <i>D.C.</i> ductus Cuvieri, <i> +S.Ca.V.</i> and <i>V.Ca.</i> fore and hind cardinal veins.</td> +</tr> +</table> +</center> + +<br> + + +<p>The fore-end of the spindle-shaped tube, which soon bends into +an S-shape (Figure 1.202), divides into a right and left branch. +These tubes are bent upwards arch-wise, and represent the first +arches of the aorta. They rise in the wall of the fore-gut, which +they enclose in a sense, and then unite above, in the upper wall of +the fore gut-cavity, to form a large single artery, that runs +backward immediately under the chorda, and is called the aorta +(Fig. 201 <i>Ao</i>). The first pair of aorta-arches rise on the +inner wall of the first pair of gill-arches, and so lie between the +first gill-arch (<i>k</i>) and the fore-gut (<i>d</i>), just as we +find them throughout life in the fishes. The single aorta, which +results from the conjunction of these two first vascular arches, +divides again immediately into two parallel branches, which run +backwards on either side of the chorda. These are the primitive +aortas which we have already mentioned; they are also called the +posterior vertebral arteries. These two arteries now give off at +each side, behind, at right angles, four or five branches, and +these pass from the embryonic body to the germinative area, +they</p> + +<br> +<hr> +<p class="page"><a name="page 171">[ 171 ]</a></p> + +<p> </p> + +<p class="one">are called omphalo-mesenteric or vitelline arteries. +They represent the first beginning of a fœtal circulation. +Thus, the first blood-vessels pass over the embryonic body and +reach as far as the edge of the germinative area. At first they are +confined to the dark or “vascular” area. But they +afterwards extend over the whole surface of the embryonic vesicle. +In the end, the whole of the yelk-sac is covered with a vascular +net-work. These vessels have to gather food from the contents of +the yelk-sac and convey it to the embryonic body. This is done by +the veins, which pass first from the germinative area, and +afterwards from the yelk-sac, to the farther end of the heart. They +are called vitelline, or, frequently, omphalo-mesenteric, +veins.</p> + +<p>These vessels naturally atrophy with the degeneration of the +umbilical vesicle, and the vitelline circulation is replaced by a +second, that of the allantois. Large blood-vessels are developed in +the wall of the urinary sac or the allantois, as before, from the +gut-fibre layer. These vessels grow larger and larger, and are very +closely connected with the vessels that develop in the body of the +embryo itself. Thus, the secondary, allantoic circulation gradually +takes the place of the original vitelline circulation. When the +allantois has attached itself to the inner wall of the chorion and +been converted into the placenta, its blood-vessels alone effect +the nourishment of the embryo. They are called umbilical vessels, +and are originally double—a pair of umbilical arteries and a +pair of umbilical veins. The two umbilical veins <a href= +"#Fig. 183">(Fig. 183 <i>u</i>),</a> which convey blood from the +placenta to the heart, open it first into the united vitelline +veins. The latter then disappear, and the right umbilical vein goes +with them, so that henceforth a single large vein, the left +umbilical vein, conducts all the blood from the placenta to the +heart of the embryo. The two arteries of the allantois, or the +umbilical arteries (Figs. 183 <i>n</i>, 184 <i>n</i>), are merely +the ultimate terminations of the primitive aortas, which are +strongly developed afterwards. This umbilical circulation is +retained until the nine months of embryonic life are over, and the +human embryo enters into the world as the independent individual. +The umbilical cord (Fig. 196 <i>al</i>), in which these large +blood-vessels pass from the embryo to the placenta, comes away, +together with the latter, in the after-birth, and with the use of +the lungs begins an entirely new form of circulation, which is +confined to the body of the infant.</p> + + +<table class="capt" width="222" align="left" summary= +"Fig. 202. Boat-shaped embryo of the dog, from the ventral side, magnified."> +<tr> +<td><img src="images2/fig202.GIF" width="222" height="271" alt= +"Boat-shaped embryo of the dog, from the ventral side, magnified."> +<a name="Fig. 202">Fig. +202</a>—<b>Boat-shaped embryo of the dog,</b> from the +ventral side, magnified. In front under the forehead we can see the +first pair of gill-arches; underneath is the S-shaped heart, at the +sides of which are the auditory vesicles. The heart divides behind +into the two vitelline veins, which expand in the germinative area +(which is torn off all round). On the floor of the open belly lie, +between the protovertebræ, the primitive aortas, from which +five pairs of vitelline arteries are given off. (From <i> +Bischoff.</i>)</td> +</tr> +</table> + + +<p>There is a great phylogenetic significance in the perfect +agreement which we find between man and the anthropoid apes in +these important features of embryonic circulation, and the special +construction of the placenta and the umbilical cord. We must infer +from it a close blood-relationship of man and the anthropomorphic +apes—a common descent of them from one and the same extinct +group of lower apes. Huxley’s +“pithecometra-principle” applies to these ontogenetic +features as much as to any other morphological relations: +“The differences in construction of any part of the body are +less between man and the anthropoid apes than between the latter +and the lower apes.”</p> + +<p>This important Huxleian law, the chief consequence of which is +“the descent of man from the ape,” has lately been +confirmed in an interesting and unexpected way from the side of the +experimental</p> + +<br> +<hr> +<p class="page"><a name="page 172">[ 172 ]</a></p> + +<p> </p> + +<p class="one">physiology of the blood. The experiments of Hans +Friedenthal at Berlin have shown that human blood, mixed with the +blood of lower apes, has a poisonous effect on the latter; the +serum of the one destroys the blood-cells of the other. But this +does not happen when human blood is mixed with that of the +anthropoid ape. As we know from many other experiments that the +mixture of two different kinds of blood is only possible without +injury in the case of two closely related animals of the same +family, we have another proof of the close blood-relationship, in +the literal sense of the word, of man and the anthropoid ape.</p> + +<br> + + +<center> +<table class="capt" width="338" summary= +"Fig. 203. Lar or white-handed gibbon (Hylobates lar or albimanus), from the Indian mainland."> +<tr> +<td align="center"> +<img src="images2/fig203.GIF" width="338" height="415" alt= +"Lar or white-handed gibbon (Hylobates lar or albimanus), from the Indian mainland."> +<a name="Fig. 203">Fig. 203</a>—<b>Lar or +white-handed gibbon</b> (<i>Hylobates lar</i> or <i>albimanus</i>), +from the Indian mainland (From <i>Brehm.</i>)</td> +</tr> +</table> +</center> + +<br> +<br> + <br> +<hr> +<p class="page"><a name="page 173">[ 173 ]</a></p> + +<p> </p> + +<center> +<table class="capt" width="301" summary= +"Fig. 204. Young orang (Satyrus orang), asleep."> +<tr> +<td align="center"> +<img src="images2/fig204.GIF" width="301" height="481" alt= +"Young orang (Satyrus orang), asleep."> +<a name="Fig. 204">Fig. 204</a>—<b>Young +orang</b> (<i>Satyrus orang</i>), asleep.</td> +</tr> +</table> +</center> + +<p>The existing anthropoid apes are only a small remnant of a large +family of eastern apes (or <i>Catarrhinæ</i>), from which man +was evolved about the end of the Tertiary period. They fall into +two geographical groups—the Asiatic and the African +anthropoids. In each group we can distinguish two genera. The +oldest of these four genera is the gibbon <i>Hylobates,</i> Fig. +203); there are from eight to twelve species of it in the East +Indies. I made observations of four of them during my voyage in the +East Indies (1901), and had a specimen of the ash-grey gibbon +(<i>Hylobates leuciscus</i>) living for several months in the +garden of my house in Java. I have described the interesting habits +of this ape (regarded by the Malays as the wild descendant of men +who had lost their way) in my <i>Malayischen</i></p> + +<br> +<hr> +<p class="page"><a name="page 174">[ 174 ]</a></p> + +<p> </p> + +<p class="one"><i>Reisebriefen</i> (chap. xi). Psychologically, he +showed a good deal of resemblance to the children of my Malay +hosts, with whom he played and formed a very close friendship.</p> + +<br> + + +<center> +<table class="capt" width="414" summary= +"Fig. 205. Wild orang (Dyssatyrus auritus)."> +<tr> +<td align="center"> +<img src="images2/fig205.GIF" width="414" height="411" alt= +"Wild orang (Dyssatyrus auritus)."> +<a name="Fig. 205">Fig. 205</a>—<b>Wild +orang</b> (<i>Dyssatyrus auritius</i>). (From <i>R. Fick</i> and +<i>Leutemann.</i>).</td> +</tr> +</table> +</center> + +<p>The second, larger and stronger, genus of Asiatic anthropoid ape +is the orang (<i>Satyrus</i>); he is now found only in the islands +of Borneo and Sumatra. Selenka, who has published a very thorough +<i>Study of the Development and Cranial Structure of the Anthropoid +Apes</i> (1899), distinguishes ten races of the orang, which may, +however, also be regarded as “local varieties or +species.” They fall into two sub-genera or genera: one group, +<i>Dyssatyrus</i> (orang-bentang, Fig. 205), is distinguished for +the strength of its limbs, and the formation of very peculiar and +salient cheek-pads in the elderly male; these are wanting in the +other group, the ordinary orang-outang (<i>Eusatyrus</i>).</p> + +<p>Several species have lately been distinguished in the two genera +of the black African anthropoid apes (chimpanzee and gorilla). In +the genus <i>Anthropithecus</i> (or <i>Anthropopithecus,</i> +formerly <i>Troglodytes</i>), the bald-headed chimpanzee, <i>A. +calvus</i> (Fig. 206), and the gorilla-like <i>A. mafuca</i> differ +very strikingly from the ordinary <i>Anthropithecus niger</i> (Fig. +207), not only in the size and proportion of many parts of the +body, but also in the peculiar shape of the head, especially the +ears and lips, and in the hair and colour. The controversy that +still continues as to whether these different forms of</p> + +<br> +<hr> +<p class="page"><a name="page 175">[ 175 ]</a></p> + +<p> </p> + +<center> +<table class="capt" width="362" summary= +"Fig. 206. The bald-headed chimpanzee (Anthropithecus calvus). Female."> +<tr> +<td align="justify"> +<img src="images2/fig206.GIF" width="362" height="445" alt= +"The bald-headed chimpanzee (Anthropithecus calvus). Female."> +<a name="Fig. 206">Fig. 206</a>—<b>The +bald-headed chimpanzee</b> (<i>Anthropithecus calvus</i>). Female. +This fresh species, described by Frank Beddard in 1897 as +Troglodytes calvus, differs considerably from the ordinary <i>A. +niger</i> Fig. 207) in the structure of the head, the colouring, +and the absence of hair in parts.</td> +</tr> +</table> +</center> + +<br> +<br> + <br> +<hr> +<p class="page"><a name="page 176">[ 176 ]</a></p> + +<p> </p> + +<p class="one">chimpanzee and orang are “merely local +varieties” or “true species” is an idle one; as +in all such disputes of classifiers there is an utter absence of +clear ideas as to what a species really is.</p> + +<p>Of the largest and most famous of all the anthropoid apes, the +gorilla, Paschen has lately discovered a giant-form in the interior +of the Cameroons, which seems to differ from the ordinary species +(<i>Gorilla gina</i> Fig. 208), not only by its unusual size and +strength, but also by a special formation of the skull. This giant +gorilla (<i>Gorilla gigas,</i> Fig. 209) is six feet eight inches +long; the span of its great arms is about nine feet; its powerful +chest is twice as broad as that of a strong man.</p> + +<br> + + +<center> +<table class="capt" width="248" summary= +"Fig. 207. Female chimpanzee (Anthropithecus niger)."> +<tr> +<td align="center"> +<img src="images2/fig207.GIF" width="248" height="327" alt= +"Female chimpanzee (Anthropithecus niger)."> +<a name="Fig. 207">Fig. 207</a>—<b>Female +chimpanzee</b> (<i>Anthropithecus niger</i>). (From <i> +Brehm.</i>)</td> +</tr> +</table> +</center> + +<p>The whole structure of this huge anthropoid ape is not merely +very similar to that of man, but it is substantially the same. +“The same 200 bones, arranged in the same way, form our +internal skeleton; the same 300 muscles effect our movements; the +same hair covers our skin; the same groups of ganglionic cells +compose the ingenious mechanism of our brain; the same +four-chambered heart is the central pump of our circulation.” +The really existing differences in the shape and size of the +various parts are explained by differences in their growth, due to +adaptation to different habits of life and unequal use of the +various organs. This of itself proves morphologically the descent +of man from the ape. We will return to the point in Chapter XXIII. +But I wanted to point already to this important solution of +“the question of questions,” because that agreement</p> + +<br> +<hr> +<p class="page"><a name="page 177">[ 177 ]</a></p> + +<p> </p> + +<p class="one">in the formation of the embryonic membranes and in +fœtal circulation which I have described affords a +particularly weighty proof of it. It is the more instructive as +even cenogenetic structures may in certain circumstances have a +high phylogenetic value. In conjunction with the other facts, it +affords a striking confirmation of our biogenetic law.</p> + +<br> + + +<center> +<table class="capt" width="230" summary= +"Fig. 208. Female gorilla.."> +<tr> +<td align="center"> +<img src="images2/fig208.GIF" width="230" height="353" alt= +"Female gorilla."> +<a name="Fig. 208">Fig. 208</a>—<b>Female +gorilla.</b> (From <i>Brehm.</i>).</td> +</tr> +</table> +</center> + +<br> +<br> + <br> +<hr> +<p class="page"><a name="page 178">[ 178 ]</a></p> + +<p> </p> + +<center> +<table class="capt" width="327" summary= +"Fig. 209. Male giant-gorilla (Gorilla gigas), from Yaunde, in the interior of the Cameroons. Killed by H. Paschen, stuffed by Umlauff."> +<tr> +<td align="center"> +<img src="images2/fig209.GIF" width="327" height="523" alt= +"Male giant-gorilla (Gorilla gigas), from Yaunde, in the interior of the Cameroons. Killed by H. Paschen, stuffed by Umlauff."> +<a name="Fig. 209">Fig. 209</a>—<b>Male +giant-gorilla</b> (<i>Gorilla gigas</i>), from Yaunde, in the +interior of the Cameroons. Killed by H. Paschen, stuffed by +Umlauff.</td> +</tr> +</table> +</center> + +<br> + + +<hr noshade align="left" size="1" width="20%"> +<p class="ref"><a href="Title.html">Title and Contents</a><br> +<a href="glossary.html">Glossary</a><br> +<a href="chap14.html">Chapter XIV</a><br> +<a href="title2.html">Vol. II Title</a><br> +<a href="Title.html#Illustrations">Figs. 1–209</a><br> +<a href="title2.html#Illustrations">Figs. 210–408</a></p> +</body> +</html> + |