COMPARATIVE ANATOMY. 



indifferently, and agglutinated by their 

 surfaces, which determine the order of 

 their arrangement : living bodies, on the 

 contrary, consist of numerous fibres or 

 laminae, of heterogenous composition, and 

 various figures, each of which has its pe- 

 culiar situation in relation to the other 

 fibres and laminae. Moreover, from the 

 instant in which a living body can be said 

 to exist, however small it may be, it 

 possesses all its parts ; it does not grow 

 by the addition of any new laminre, but 

 by the uniform or irregular devclopement 

 of parts which existed before any sensi- 

 ble growth. 



The only circumstance common to all 

 generation, and, consequently, the only 

 essential part of the process, is, that 

 every living body is attached at first to 

 a larger body of the same species with 

 itself. It constitutes a part of this larger 

 body, and derives nourishment for a cer- 

 tain time from its juices. The subsequent 

 separation constitutes birth ; and may be 

 the simple result of the life of the larger 

 body, and of the consequent develope- 

 ment of the smaller, without the addition 

 of any occasional action. 



Thus the essence of generation con- 

 sists in the appearance of a small organ- 

 ised body in or upon some part of a larger 

 one ; from which it is separated at a cer- 

 tain period, in order to assume an inde- 

 pendent existence. 



All the processes and organs, which co- 

 operate in the business of generation in 

 certain classes, are only accessory to this 

 primary function. 



When the function is thus reduced to 

 its most simple state, it constitutes the 

 g-emmiparous, or generation by shoots. 

 In this way the buds of trees are develop- 

 ed into branches, from which other trees 

 may be formed. The polypes (hydra) 

 and the sea-anemones (actinia) multiply 

 in this manner ; some worms are propa- 

 gated by a division of their body, and 

 must therefore be arranged in the same 

 division. This mode of generation re- 

 quires no distinction of sex, no copula- 

 tion, nor any particular organ. 



Other modes of generation are accom- 

 plished inappropriate organs : the gvrms 

 appear in a definite situation in the body, 

 and the assistance of certain operations 

 is required for their further develope- 

 ment. These operations constitute fecun- 

 dation, and suppose the existence of 

 sexual parts : which may either be sepa- 

 rate, or united in the same individual. 



The office of the male sex is that of 

 furnishing the fecundating or seminal 

 fluid; but the manner in which that 



contributes to the devclopement of the 

 germ is not yet settled by physiologists. 

 Some, forming their opinions from the 

 human subject and the mammalia, where 

 the germs are imperceptible before fe- 

 cundation, suppose that these are creat- 

 ted by the mixture of the male fluid with 

 that which they suppose to exist in tht: 

 female ; or that they pre-exist in the mule 

 semen, and that the female only furnishes 

 them with an abode. Others consult the 

 analogy of the other classes of animals 

 and of plants. In several instances, par- 

 ticularly in the frog, the germ may be 

 clearly recognised in the ovum, before 

 fecundation : its pre-existence may be 

 concluded, in other cases, from the man- 

 ner in which it is connected to the ovum 

 when it first becomes visible ; for it is 

 agreed on* all sides, that the ovum exists 

 in the female before fecundation, since 

 virgin hens lay eggs, &c. From such 

 considerations these physiologists con- 

 clude, that the germ pre-exists in all fe- 

 males, and that the fecundating liquor 

 is a stimulus, which bestows on it an in- 

 dependent life, by awakening it, in a 

 manner, from the species of lethargy in 

 which it would otherwise have constantly- 

 remained. 



The origin of the germs, and the mode 

 of their existence in the female, whether 

 they are formed anew by the action of 

 life, or are prc-existent, and inclosed 

 within each other; or whether they are 

 disseminated, and require a concourse of 

 circumstances to bring them into a situa- 

 tion favourable for their developement ; 

 are questions, which, in the present state 

 of our knowledge, it is utterly impossible 

 for us to decide. These points have fora 

 long time been agitated by physiologists; 

 but the discussion seems now to be aban- 

 doned by universal consent. 



The combination of the sexes, and the 

 mode of fecundation, are subject to great 

 variety. In some instances they are 

 united in the same individual, and the 

 animal impregnates itself. The acepha- 

 lous mollusca and the echinus exemplify 

 this structure. In others, although the 

 sexes are united in each individual, an 

 act of copulation is required, in which 

 they both fecundate and are fecundated. 

 This is the case with the gasteropodous 

 mollusca, and several worms. In the re- 

 mainder of the animal kingdom the sexes 

 belong to different individuals. 



The fecundating liquor is always ap- 

 plied upon or about the germs. In many 

 cases the ova are laid before they are 

 touched by the semen ; as in some fishes 

 of the bony division, and the cephalopo- 



