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diff --git a/8700-h/old/chap7.html b/8700-h/old/chap7.html new file mode 100644 index 0000000..5c5ba11 --- /dev/null +++ b/8700-h/old/chap7.html @@ -0,0 +1,749 @@ +<!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> VII<br> +<br> +<b>CONCEPTION</b></center> + +<br> + + +<p class="one">The recognition of the fact that every man begins +his individual existence as a simple cell is the solid foundation +of all research into the genesis of man. From this fact we are +forced, in virtue of our biogenetic law, to draw the weighty +phylogenetic conclusion that the earliest ancestors of the human +race were also unicellular organisms; and among these protozoa we +may single out the vague form of the amœba as particularly +important (cf. Chapter VI). That these unicellular ancestral forms +did once exist follows directly from the phenomena which we +perceive every day in the fertilised ovum. The development of the +multicellular organism from the ovum, and the formation of the +germinal layers and the tissues, follow the same laws in man and +all the higher animals. It will, therefore, be our next task to +consider more closely the impregnated ovum and the process of +conception which produces it.</p> + +<p>The process of impregnation or sexual conception is one of those +phenomena that people love to conceal behind the mystic veil of +supernatural power. We shall soon see, however, that it is a purely +mechanical process, and can be reduced to familiar physiological +functions. Moreover, this process of conception is of the same +type, and is effected by the same organs, in man as in all the +other mammals. The pairing of the male and female has in both cases +for its main purpose the introduction of the ripe matter of the +male seed or sperm into the female body, in the sexual canals of +which it encounters the ovum. Conception then ensues by the +blending of the two.</p> + +<p>We must observe, first, that this important process is by no +means so widely distributed in the animal and plant world as is +commonly supposed. There is a very large number of lower organisms +which propagate unsexually, or by monogamy; these are especially +the sexless monera (chromacea, bacteria, etc.) but also many other +protists, such as the amœbæ, foraminifera, radiolaria, +myxomycetæ, etc. In these the multiplication of individuals +takes place by unsexual reproduction, which takes the form of +cleavage, budding, or spore-formation. The copulation of two +coalescing cells, which in these cases often precedes the +reproduction, cannot be regarded as a sexual act unless the two +copulating plastids differ in size or structure. On the other hand, +sexual reproduction is the general rule with all the higher +organisms, both animal and plant; very rarely do we find asexual +reproduction among them. There are, in particular, no cases of +parthenogenesis (virginal conception) among the vertebrates.</p> + +<p>Sexual reproduction offers an infinite variety of interesting +forms in the different classes of animals and plants, especially as +regards the mode of conception, and the conveyance of the +spermatozoon to the ovum. These features are of great importance +not only as regards conception itself, but for the development of +the organic form, and especially for the differentiation of the +sexes. There is a particularly curious correlation of plants and +animals in this respect. The splendid studies of Charles Darwin and +Hermann Müller on the fertilisation of flowers by insects have +given us very interesting particulars of this.<sup>1</sup> This +reciprocal service has given rise to a most intricate sexual +apparatus. Equally elaborate structures have been developed in man +and the higher animals, serving partly for the isolation of the +sexual products on each side, partly for bringing them together in +conception. But, however interesting these phenomena are in +themselves, we cannot go into them here, as they have only a minor +importance—if any at all—in the real process of +conception. We must, however, try to get a very clear idea of this +process and the meaning of sexual reproduction.</p> + +<p class="fnote">1. See Darwin’s work, <i>On the Various +Contrivances by which Orchids are Fertilised</i> (1862).</p> + +<br> +<hr> +<p class="page"><a name="page 52">[ 52 ]</a></p> + +<p> </p> + +<p class="one">In every act of conception we have, as I said, to +consider two different kinds of cells—a female and a male +cell. The female cell of the animal organism is always called the +ovum (or <i>ovulum,</i> egg, or egg-cell); the male cells are known +as the sperm or seed-cells, or the spermatozoa (also spermium and +zoospermium). The ripe ovum is, on the whole, one of the largest +cells we know. It attains colossal dimensions when it absorbs great +quantities of nutritive yelk, as is the case with birds and +reptiles and many of the fishes. In the great majority of the +animals the ripe ovum is rich in yelk and much larger than the +other cells. On the other hand, the next cell which we have to +consider in the process of conception, the male sperm-cell or +spermatozoon, is one of the smallest cells in the animal body. +Conception usually consists in the bringing into contact with the +ovum of a slimy fluid secreted by the male, and this may take place +either inside or out of the female body. This fluid is called +sperm, or the male seed. Sperm, like saliva or blood, is not a +simple fluid, but a thick agglomeration of innumerable cells, +swimming about in a comparatively small quantity of fluid. It is +not the fluid, but the independent male cells that swim in it, that +cause conception.</p> + +<br> + + +<center> +<table class="capt" width="356" cellspacing="0" summary= +"Fig. 20--Spermia or spermatozoa of various mammals."> +<tr> +<td width="356"><img src="images/fig20.GIF" width="356" height="212" alt= +"Fig. 20--Spermia or spermatozoa of various mammals."><br><br> +<a name="Fig. 20">Fig. 20</a>—<b>Spermia or +spermatozoa of various mammals.</b> The pear-shaped flattened +nucleus is seen from the front in <i>I</i> and sideways in <i>II. +k</i> is the nucleus, <i>m</i> its middle part (protoplasm), <i> +s</i> the mobile, serpent-like tail (or whip); <i>M</i> four human +spermatozoa, <i>A</i> four spermatozoa from the ape; <i>K</i> from +the rabbit; <i>H</i> from the mouse; <i>C</i> from the dog; <i> +S</i> from the pig.</td> +</tr> +</table> +</center> + +<p>The spermatozoa of the great majority of animals have two +characteristic features. Firstly, they are extraordinarily small, +being usually the smallest cells in the body; and, secondly, they +have, as a rule, a peculiarly lively motion, which is known as +spermatozoic motion. The shape of the cell has a good deal to do +with this motion. In most of the animals, and also in many of the +lower plants (but not the higher) each of these spermatozoa has a +very small, naked cell-body, enclosing an elongated nucleus, and a +long thread hanging from it (Fig. 20). It was long before we could +recognise that these structures are simple cells. They were +formerly held to be special organisms, and were called “seed +animals” (spermato-zoa, or spermato-zoidia); they are now +scientifically known as <i>spermia</i> or <i>spermidia,</i> or as +<i>spermatosomata</i> (seed-bodies) or <i>spermatofila</i> (seed +threads). It took a good deal of comparative research to convince +us that each of these spermatozoa is really a simple cell. They +have the same shape as in many other vertebrates and most of the +invertebrates. However, in many of the lower animals they have +quite a different shape. Thus, for instance, in the craw fish they +are large round cells, without any movement, equipped with stiff +outgrowths like bristles <a href="#Fig. 21">(Fig. 21 <i> +f</i> ).</a> They have also a peculiar form in some of the +worms, such as the thread-worms (<i>filaria</i>); in this case they +are sometimes</p> + +<br> +<hr> +<p class="page"><a name="page 53">[ 53 ]</a></p> + +<p> </p> + +<p class="one">amœboid and like very small ova (Fig. 21 <i> +c</i> to <i>e</i>). But in most of the lower animals (such as the +sponges and polyps) they have the same pine-cone shape as in man +and the other animals (Fig. 21 <i>a, h</i>).</p> + +<br> + + +<table class="capt" width="236" align="left" summary= +"Fig. 21--Spermatozoa or spermidia of various animals."> +<tr> +<td align="justify"><img src="images/fig21.GIF" width="236" height="154" alt= +"Fig. 21--Spermatozoa or spermidia of various animals."> +<a name="Fig. 21">Fig. 21</a>—<b>Spermatozoa +or spermidia of various animals.</b> (From <i>Lang</i>). <i>a</i> +of a fish, <i>b</i> of a turbellaria worm (with two side-lashes), +<i>c</i> to <i>e</i> of a nematode worm (amœboid +spermatozoa), <i>f</i> from a craw fish (star-shaped), <i>g</i> +from the salamander (with undulating membrane), <i>h</i> of an +annelid (<i>a</i> and <i>h</i> are the usual shape).</td> +</tr> +</table> + +<p class="pic">When the Dutch naturalist Leeuwenhoek discovered these +thread-like lively particles in 1677 in the male sperm, it was +generally believed that they were special, independent, tiny +animalcules, like the infusoria, and that the whole mature organism +existed already, with all its parts, but very small and packed +together, in each spermatozoon (see <a href="chap2.html#page 12"> +p.12</a>). We now know that the mobile spermatozoa are nothing but +simple and real cells, of the kind that we call +“ciliated” (equipped with lashes, or <i>cilia</i>). In +the previous illustrations we have distinguished in the +spermatozoon a head, trunk, and tail. The “head” <a +href="#Fig. 20">(Fig. 20 <i>k</i>)</a> is merely the oval nucleus +of the cell; the body or middle-part (<i>m</i>) is an accumulation +of cell-matter; and the tail (<i>s</i>) is a thread-like +prolongation of the same.</p> + +<p>Moreover, we now know that these spermatozoa are not at all a +peculiar form of cell; precisely similar cells are found in various +other parts of the body. If they have many short threads +projecting, they are called <i>ciliated</i>; if only one long, +whip-shaped process (or, more rarely, two or four), <i>caudate</i> +(tailed) cells.</p> + +<p>Very careful recent examination of the spermia, under a very +high microscopic power (Fig. 22 a, b), has detected some further +details in the finer structure of the ciliated cell, and these are +common to man and the anthropoid ape. The head (<i>k</i>) encloses +the elliptic nucleus in a thin envelope of cytoplasm; it is a +little flattened on one side, and thus looks rather pear-shaped +from the front (<i>b</i>). In the central piece (<i>m</i>) we can +distinguish a short neck and a longer connective piece (with +central body). The tail consists of a long main section (<i>h</i>) +and a short, very fine tail (<i>e</i>).</p> + + +<table class="capt" width="184" align="left" summary= +"Fig. 22--A single human spermatozoon."> +<tr> +<td align="justify"><img src="images/fig22.GIF" width="184" height="300" alt= +"Fig. 22--A single human spermatozoon."> +<a name="Fig. 22">Fig. 22</a>—<b>A single +human spermatozoon</b> magnified; a shows it from the broader and b +from the narrower side. <i>k</i> head (with nucleus), <i>m</i> +middle-stem, <i>h</i> long-stem, and <i>e</i> tail. (From <i> +Retzius.</i>)</td> +</tr> +</table> + +<p class="pic">The process of fertilisation by sexual conception consists, +therefore, essentially in the coalescence and fusing together of +two different cells. The lively spermatozoon travels towards the +ovum by its serpentine movements, and bores its way into the female +cell <a href="#Fig. 23">(Fig. 23).</a> The nuclei of both sexual +cells, attracted by a certain “affinity,” approach each +other and melt into one.</p> + +<p>The fertilised cell is quite another thing from the unfertilised +cell. For if we must regard the spermia as real cells no less than +the ova, and the process of conception as a coalescence of the two, +we must consider the resultant cell as a quite new and independent +organism. It bears in the cell and nuclear matter of the +penetrating spermatozoon a part of the father’s body, and in +the protoplasm and caryoplasm of the ovum a part of the +mother’s body. This is clear from the fact that the child +inherits many features from both parents. It inherits from the +father by means of the spermatozoon, and from the mother by means +of the ovum. The</p> + +<br> +<hr> +<p class="page"><a name="page 54">[ 54 ]</a></p> + +<p> </p> + +<p class="one">actual blending of the two cells produces a third +cell, which is the germ of the child, or the new organism +conceived. One may also say of this sexual coalescence that the <i> +stem-cell is a simple hermaphrodite</i>; it unites both sexual +substances in itself.</p> + + +<table class="capt" width="216" align="left" summary= +"Fig. 23--The fertilisation of the ovum by the spermatozoon."> +<tr> +<td align="justify"><img src="images/fig23.GIF" width="216" height="164" +alt="Fig. 23--The fertilisation of the ovum by the spermatozoon."> +<a name="Fig. 23">Fig. 23</a>—<b>The fertilisation of the ovum by the spermatozoon</b> (of a mammal). One of the many thread-like, lively spermidia pierces through a fine pore-canal into the nuclear yelk. The nucleus of the ovum is invisible.</td> +</tr> +</table> + +<p class="pic">I think it necessary to emphasise the fundamental importance of +this simple, but often unappreciated, feature in order to have a +correct and clear idea of conception. With that end, I have given a +special name to the new cell from which the child develops, and +which is generally loosely called “the fertilised +ovum,” or “the first segmentation sphere.” I call +it “the stem-cell” (<i>cytula</i>). The name +“stem-cell” seems to me the simplest and most suitable, +because all the other cells of the body are derived from it, and +because it is, in the strictest sense, the stem-father and +stem-mother of all the countless generations of cells of which the +multicellular organism is to be composed. That complicated +molecular movement of the protoplasm which we call +“life” is, naturally, something quite different in this +stem-cell from what we find in the two parent-cells, from the +coalescence of which it has issued. <i>The life of the stem-cell or +cytula is the product or resultant of the paternal life-movement +that is conveyed in the spermatozoon and the maternal life-movement +that is contributed by the ovum.</i></p> + +<p>The admirable work done by recent observers has shown that the +individual development, in man and the other animals, commences +with the formation of a simple “stem-cell” of this +character, and that this then passes, by repeated segmentation (or +cleavage), into a cluster of cells, known as “the +segmentation sphere” or “segmentation cells.” The +process is most clearly observed in the ova of the echinoderms +(star-fishes, sea-urchins, etc.). The investigations of Oscar and +Richard Hertwig were chiefly directed to these. The main results +may be summed up as follows:—</p> + +<p>Conception is preceded by certain preliminary changes, which are +very necessary—in fact, usually indispensable—for its +occurrence. They are comprised under the general heading of +“Changes prior to impregnation.” In these the original +nucleus of the ovum, the germinal vesicle, is lost. Part of it is +extruded, and part dissolved in the cell contents; only a very +small part of it is left to form the basis of a fresh nucleus, the +<i>pronucleus femininus.</i> It is the latter alone that combines +in conception with the invading nucleus of the fertilising +spermatozoon (the <i>pronucleus masculinus</i>).</p> + +<p>The impregnation of the ovum commences with a decay of the +germinal vesicle, or the original nucleus of the ovum <a href= +"chap6.html#Fig. 8">(Fig. 8).</a> We have seen that this is in most +unripe ova a large, transparent, round vesicle. This germinal +vesicle contains a viscous fluid (the <i>caryolymph</i>). The firm +nuclear frame (<i>caryobasis</i>) is formed of the enveloping +membrane and a mesh-work of nuclear threads running across the +interior, which is filled with the nuclear sap. In a knot of the +network is contained the dark, stiff, opaque nuclear corpuscle or +nucleolus. When the impregnation of the ovum sets in, the greater +part of the germinal vesicle is dissolved in the cell; the nuclear +membrane and mesh-work disappear; the nuclear sap is distributed in +the protoplasm; a small portion of the nuclear base is extruded; +another small portion is left, and is converted into the secondary +nucleus, or the female pro-nucleus <a href="#Fig. 24">(Fig. 24 <i>e +k</i>).</a></p> + +<p>The small portion of the nuclear base which is extruded from the +impregnated ovum is known as the “directive bodies” or +“polar cells”; there are many disputes as to their +origin and significance, but we are as yet imperfectly acquainted +with them. As a rule, they are two small round granules, of the +same size and appearance as the remaining pro-nucleus. They are +detached cell-buds; their separation from the large mother-cell +takes</p> + +<br> +<hr> +<p class="page"><a name="page 55">[ 55 ]</a></p> + +<p> </p> + +<p class="one">place in the same way as in ordinary “indirect +cell-division.” Hence, the polar cells are probably to be +conceived as “abortive ova,” or “rudimentary +ova,” which proceed from a simple original ovum by cleavage +in the same way that several sperm-cells arise from one +“sperm-mother-cell,” in reproduction from sperm. The +male sperm-cells in the testicles must undergo similar changes in +view of the coming impregnation as the ova in the female ovary. In +this maturing of the sperm each of the original seed-cells divides +by double segmentation into four daughter-cells, each furnished +with a fourth of the original nuclear matter (the hereditary +chromatin); and each of these four descendant cells becomes a <i> +spermatozoon,</i> ready for impregnation. Thus is prevented the +doubling of the chromatin in the coalescence of the two nuclei at +conception. As the two polar cells are extruded and lost, and have +no further part in the fertilisation of the ovum, we need not +discuss them any further. But we must give more attention to the +female pro-nucleus which alone remains after the extrusion of the +polar cells and the dissolving of the germinal vesicle <a href= +"#Fig. 23">(Fig. 23 <i>e k</i>).</a> This tiny round corpuscle of +chromatin now acts as a centre of attraction for the invading +spermatozoon in the large ripe ovum, and coalesces with its +“head,” the male pro-nucleus. The product of this +blending, which is the most important part of the act of +impregnation, is the stem-nucleus, or the first segmentation +nucleus (<i>archicaryon</i>)—that is to say, the nucleus of +the new-born embryonic stem-cell or “first segmentation +cell.” This stem-cell is the starting point of the subsequent +embryonic processes.</p> + +<p>Hertwig has shown that the tiny transparent ova of the +echinoderms are the most convenient for following the details of +this important process of impregnation. We can, in this case, +easily and successfully accomplish artificial impregnation, and +follow the formation of the stem-cell step by step within the space +of ten minutes. If we put ripe ova of the star-fish or sea-urchin +in a watch glass with sea-water and add a drop of ripe sperm-fluid, +we find each ovum impregnated within five minutes. Thousands of the +fine, mobile ciliated cells, which we have described as +“sperm-threads” <a href="#Fig. 20">(Fig. 20),</a> make +their way to the ova, owing to a sort of chemical sensitive action +which may be called “smell.” But only one of these +innumerable spermatozoa is chosen—namely, the one that first +reaches the ovum by the serpentine motions of its tail, and touches +the ovum with its head. At the spot where the point of its head +touches the surface of the ovum the protoplasm of the latter is +raised in the form of a small wart, the “impregnation +rise” <a href="#Fig. 25">(Fig. 25 <i>A</i>).</a> The +spermatozoon then bores its way into this with its head, the tail +outside wriggling about all the time (Fig. 25 <i>B, C</i>). +Presently the tail also disappears within the ovum. At the same +time the ovum secretes a thin external yelk-membrane (Fig. 25 <i> +C</i>), starting from the point of impregnation; and this prevents +any more spermatozoa from entering.</p> + +<table class="capt" width="159" align="left" summary= +"Fig. 24--An impregnated echinoderm ovum."> +<tr> +<td align="center"><img src="images/fig24.GIF" width="159" height="142" alt= +"Fig. 24--An impregnated echinoderm ovum."> +<a name="Fig. 24">Fig. 24</a>—<b>An +impregnated echinoderm ovum,</b> with small homogeneous nucleus +(<i>e k</i>).<br>(From <i>Hertwig.</i>)</td> +</tr> +</table> + +<p class="pic">Inside the impregnated ovum we now see a rapid series of most +important changes. The pear-shaped head of the sperm-cell, or the +“head of the spermatozoon,” grows larger and rounder, +and is converted into the male pro-nucleus <a href="#Fig. 26">(Fig. +26 <i>s k</i>).</a> This has an attractive influence on the fine +granules or particles which are distributed in the protoplasm of +the ovum; they arrange themselves in lines in the figure of a star. +But the attraction or the “affinity” between the two +nuclei is even stronger. They move towards each other inside the +yelk with increasing speed, the male <a href="#Fig. 26">(Fig. 27 +<i>s k</i>)</a> going more quickly than the female nucleus (<i>e +k</i>). The tiny male nucleus takes with it the radiating mantle +which spreads like a star about it. At last the two sexual nuclei +touch (usually in the centre of the globular ovum), lie close +together, are flattened at the points of contact, and coalesce into +a common mass. The small central particle of</p> + +<br> +<hr> +<p class="page"><a name="page 56">[ 56 ]</a></p> + +<p> </p> + +<p class="one">nuclein which is formed from this combination of the +nuclei is the stem-nucleus, or the first segmentation nucleus; the +new-formed cell, the product of the impregnation, is our stem-cell, +or “first segmentation sphere” <a href= +"chap6.html#Fig. 2">(Fig. 2).</a></p> + +<br> + + +<center> +<table class="capt" width="376" cellpadding="0" cellspacing="0" +summary="Fig. 25--Impregnation of the ovum of a star-fish."> +<tr> +<td><img src="images/fig25.GIF" width="376" height="160" alt= +"Fig. 25--Impregnation of the ovum of a star-fish."><br><br> +<a name="Fig. 25">Fig. 25</a>—<b>Impregnation of the ovum +of a star-fish.</b> (From <i>Hertwig.</i>) Only a small part of the +surface of the ovum is shown. One of the numerous spermatozoa +approaches the “impregnation rise” (<i>A</i>), touches +it (<i>B</i>), and then penetrates into the protoplasm of the ovum +(<i>C</i>).</td> +</tr> +</table> +</center> + +<p>Hence the one essential point in the process of sexual +reproduction or impregnation is the formation of a new cell, the +stem-cell, by the combination of two originally different cells, +the female ovum and the male spermatozoon. This process is of the +highest importance, and merits our closest attention; all that +happens in the later development of this first cell and in the life +of the organism that comes of it is determined from the first by +the chemical and morphological composition of the stem-cell, its +nucleus and its body. We must, therefore, make a very careful study +of the rise and structure of the stem-cell.</p> + +<p>The first question that arises is as to the two different active +elements, the nucleus and the protoplasm, in the actual +coalescence. It is obvious that the nucleus plays the more +important part in this. Hence Hertwig puts his theory of conception +in the principle: “Conception consists in the copulation of +two cell-nuclei, which come from a male and a female cell.” +And as the phenomenon of heredity is inseparably connected with the +reproductive process, we may further conclude that these two +copulating nuclei “convey the characteristics which are +transmitted from parents to offspring.” In this sense I had +in 1866 (in the ninth chapter of the <i>General Morphology</i>) +ascribed to the reproductive nucleus the function of generation and +<i>heredity,</i> and to the nutritive protoplasm the duties of +nutrition and <i>adaptation.</i> As, moreover, there is a complete +coalescence of the mutually attracted nuclear substances in +conception, and the new nucleus formed (the stem-nucleus) is the +real starting-point for the development of the fresh organism, the +further conclusion may be drawn that the male nucleus conveys to +the child the qualities of the father, and the female nucleus the +features of the mother. We must not forget, however, that the +protoplasmic bodies of the copulating cells also fuse together in +the act of impregnation; the cell-body of the invading spermatozoon +(the trunk and tail of the male ciliated cell) is dissolved in the +yelk of the female ovum. This coalescence is not so important as +that of the nuclei, but it must not be overlooked; and, though this +process is not so well known to us, we see clearly at least the +formation of the star-like figure (the radial arrangement of the +particles in the plasma) in it <a href="#Fig. 26">(Figs. +26–27).</a></p> + +<p>The older theories of impregnation generally went astray in +regarding the large ovum as the sole base of the new organism, and +only ascribed to the spermatozoon the work of stimulating and +originating its development. The stimulus which it gave to the ovum +was sometimes thought to be purely chemical, at other times rather +physical (on the principle of transferred movement), or again a +mystic and transcendental process. This error was partly due to the +imperfect knowledge at that time of the facts of impregnation, and +partly to the striking</p> + +<br> +<hr> +<p class="page"><a name="page 57">[ 57 ]</a></p> + +<p> </p> + +<p class="one">difference in the sizes of the two sexual cells. +Most of the earlier observers thought that the spermatozoon did not +penetrate into the ovum. And even when this had been demonstrated, +the spermatozoon was believed to disappear in the ovum without +leaving a trace. However, the splendid research made in the last +three decades with the finer technical methods of our time has +completely exposed the error of this. It has been shown that the +tiny sperm-cell is <i>not subordinated to, but coordinated +with,</i> the large ovum. The nuclei of the two cells, as the +vehicles of the hereditary features of the parents, are of equal +physiological importance. In some cases we have succeeded in +proving that the mass of the active nuclear substance which +combines in the copulation of the two sexual nuclei is originally +the same for both.</p> + +<p>These morphological facts are in perfect harmony with the +familiar physiological truth that the child inherits from both +parents, and that on the average they are equally distributed. I +say “on the average,” because it is well known that a +child may have a greater likeness to the father or to the mother; +that goes without saying, as far as the primary sexual characters +(the sexual glands) are concerned. But it is also possible that the +determination of the latter—the weighty determination whether +the child is to be a boy or a girl—depends on a slight +qualitative or quantitative difference in the nuclein or the +coloured nuclear matter which comes from both parents in the act of +conception.</p> + +<br> + + +<center> +<table class="capt" width="338" cellspacing="0" cellpadding="0" +summary= +"Figs. 26 and 27--Impregnation of the ovum of the sea-urchin."> +<tr> +<td><img src="images/fig26.GIF" width="338" height="169" alt= +"Figs. 26 and 27--Impregnation of the ovum of the sea-urchin."> +<br><br> +<a name="Fig. 26">Figs. 26 and 27.</a>—<b>Impregnation of +the ovum of the sea-urchin.</b> (From <i>Hertwig.</i>) In Fig. 26 +the little sperm-nucleus (<i>sk</i>) moves towards the larger +nucleus of the ovum (<i>ek</i>). In Fig. 27 they nearly touch, and +are surrounded by the radiating mantle of protoplasm.</td> +</tr> +</table> +</center> + +<p>The striking differences of the respective sexual cells in size +and shape, which occasioned the erroneous views of earlier +scientists, are easily explained on the principle of division of +labour. The inert, motionless ovum grows in size according to the +quantity of provision it stores up in the form of nutritive yelk +for the development of the germ. The active swimming sperm-cell is +reduced in size in proportion to its need to seek the ovum and bore +its way into its yelk. These differences are very conspicuous in +the higher animals, but they are much less in the lower animals. In +those protists (unicellular plants and animals) which have the +first rudiments of sexual reproduction the two copulating cells are +at first quite equal. In these cases the act of impregnation is +nothing more than a sudden <i>growth,</i> in which the originally +simple cell doubles its volume, and is thus prepared for +reproduction (cell-division). Afterwards slight differences are +seen in the size of the copulating cells; though the smaller ones +still have the same shape as the larger ones. It is only when the +difference in size is very pronounced that a notable difference in +shape is found: the sprightly sperm-cell changes more in shape and +the ovum in size.</p> + +<p>Quite in harmony with this new conception of the <i>equivalence +of the two gonads,</i> or the equal physiological importance of the +male and female sex-cells and their equal share in the process of +heredity, is the important fact established by Hertwig (1875), that +in normal impregnation only one single spermatozoon</p> + +<br> +<hr> +<p class="page"><a name="page 58">[ 58 ]</a></p> + +<p> </p> + +<p class="one">copulates with one ovum; the membrane which is +raised on the surface of the yelk immediately after one sperm-cell +has penetrated <a href="#Fig. 25">(Fig. 25 <i>C</i>)</a> prevents +any others from entering. All the rivals of the fortunate +penetrator are excluded, and die without. But if the ovum passes +into a morbid state, if it is made stiff by a lowering of its +temperature or stupefied with narcotics (chloroform, morphia, +nicotine, etc.), two or more spermatozoa may penetrate into its +yelk-body. We then witness <i>polyspermism.</i> The more Hertwig +chloroformed the ovum, the more spermatozoa were able to bore their +way into its unconscious body.</p><br> + +<table class="capt" width="209" align="left" summary= +"Fig. 28--Stem-cell of a rabbit."> +<tr> +<td align="justify"><img src="images/fig28.GIF" width="209" height="196" alt= +"Fig. 28--Stem-cell of a rabbit."> +<a name="Fig. 28">Fig. 28</a>—<b>Stem-cell of +a rabbit,</b> magnified. In the centre of the granular protoplasm +of the fertilised ovum (<i>d</i>) is seen the little, bright +stem-nucleus, <i>z</i> is the ovolemma, with a mucous membrane +(<i>h</i>). <i>s</i> are dead spermatozoa.</td> +</tr> +</table> + +<p class="pic">These remarkable facts of impregnation are also of the greatest +interest in psychology, especially as regards the theory of the +cell-soul, which I consider to be its chief foundation. The +phenomena we have described can only be understood and explained by +ascribing a certain lower degree of psychic activity to the sexual +principles. They <i>feel</i> each other’s proximity, and are +drawn together by a <i>sensitive</i> impulse (probably related to +smell); they <i>move</i> towards each other, and do not rest until +they fuse together. Physiologists may say that it is only a +question of a peculiar physico-chemical phenomenon, and not a +psychic action; but the two cannot be separated. Even the psychic +functions, in the strict sense of the word, are only complex +physical processes, or “psycho-physical” phenomena, +which are determined in all cases exclusively by the chemical +composition of their material substratum.</p> + +<p>The monistic view of the matter becomes clear enough when we +remember the radical importance of impregnation as regards +heredity. It is well known that not only the most delicate bodily +structures, but also the subtlest traits of mind, are transmitted +from the parents to the children. In this the chromatic matter of +the male nucleus is just as important a vehicle as the large +caryoplasmic substance of the female nucleus; the one transmits the +mental features of the father, and the other those of the mother. +The blending of the two parental nuclei determines the individual +psychic character of the child.</p> + +<p>But there is another important psychological question—the +most important of all—that has been definitely answered by +the recent discoveries in connection with conception. This is the +question of the immortality of the soul. No fact throws more light +on it and refutes it more convincingly than the elementary process +of conception that we have described. For this copulation of the +two sexual nuclei <a href="#Fig. 26">(Figs. 26 and 27)</a> +indicates the precise moment at which the individual begins to +exist. All the bodily and mental features of the new-born child are +the sum-total of the hereditary qualities which it has received in +reproduction from parents and ancestors. All that man acquires +afterwards in life by the exercise of his organs, the influence of +his environment, and education—in a word, by +adaptation—cannot obliterate that general outline of his +being which he inherited from his parents. But this hereditary +disposition, the essence of every human soul, is not +“eternal,” but “temporal”; it comes into +being only at the moment when the sperm-nucleus of the father and +the nucleus of the maternal ovum meet and fuse together. It is +clearly irrational to assume an “eternal life without +end” for an individual phenomenon, the commencement of which +we can indicate to a moment by direct visual observation.</p> + +<p>The great importance of the process of impregnation in answering +such questions is quite clear. It is true that conception has never +been studied microscopically in all its details in the human +case—notwithstanding its occurrence at every moment—for +reasons that are</p> + +<br> +<hr> +<p class="page"><a name="page 59">[ 59 ]</a></p> + +<p> </p> + +<p class="one"> +obvious enough. However, the two cells which need +consideration, the female ovum and the male spermatozoon, proceed +in the case of man in just the same way as in all the other +mammals; the human fœtus or embryo which results from +copulation has the same form as with the other animals. Hence, no +scientist who is acquainted with the facts doubts that the +processes of impregnation are just the same in man as in the other +animals.</p> + +<p>The stem-cell which is produced, and with which every man begins +his career, cannot be distinguished in appearance from those of +other mammals, such as the rabbit (Fig. 28). In the case of man, +also, this stem-cell differs materially from the original ovum, +both in regard to form (morphologically), in regard to material +composition (chemically), and in regard to vital properties +(physiologically). It comes partly from the father and partly from +the mother. Hence it is not surprising that the child who is +developed from it inherits from both parents. The vital movements +of each of these cells form a sum of mechanical processes which in +the last analysis are due to movements of the smallest vital parts, +or the molecules, of the living substance. If we agree to call this +active substance <i>plasson,</i> and its molecules <i> +plastidules,</i> we may say that the individual physiological +character of each of these cells is due to its molecular +plastidule-movement. <i>Hence, the plastidule-movement of the +cytula is the resultant of the combined plastidule-movements of the +female ovum and the male sperm-cell.</i><sup>1</sup></p> + +<p class="fnote">1. The plasson of the stem-cell or cytula may, from +the anatomical point of view, be regarded as homogeneous and +structureless, like that of the monera. This is not inconsistent +with our hypothetical ascription to the plastidules (or molecules +of the plasson) of a complex molecular structure. The complexity of +this is the greater in proportion to the complexity of the organism +that is developed from it and the length of the chain of its +ancestry, or to the multitude of antecedent processes of heredity +and adaptation.</p> + +<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="chap6.html">Chapter VI</a><br> +<a href="chap8.html">Chapter VIII</a><br> +<a href="Title.html#Illustrations">Figs. 1–209</a><br> +<a href="title2.html#Illustrations">Figs. 210–408</a></p> +</body> +</html> + |