96 The Origin and Transformation of Animals. 



being from an egg ;" and all the cases of eggless production 

 lie treats as phenomena of individual growth, assembling the 

 entire group under the new-fangled and not very happy desig- 

 nation of Geneagenesis, or the " Generation of Generations ." 

 11 Every living being/' he says, "and consequently every animal, 

 comes from a germ. With the organization of this germ com- 

 mences a series of transformations, general or partial, rapid or 

 slow, and which only terminate with its life." All animals 

 likewise undergo transformations, which, considered radically, 

 11 are due to the same cause, and are effected by the same 

 methods." The germs or first rudiments of living things may 

 be referred to three types. Animals multiply by eggs and by 

 buds, which are either permanent or "caducous."* The egg* 

 method may be regarded as " fundamental, and the distinction 

 between oviparous and viviparous species, although still 

 admitted in scientific phraseology, is in reality only nominal. 

 Baer, in discovering the egg of the mammalia, M. Coste, in 

 demonstrating that this egg possesses the same parts as the egg 

 of birds, have established this fact, which has been put out of 

 doubt by the profound researches of those two naturalists and 

 by the admirable labours of English and German physiologists, 

 Barry, Bernhardt, Bischoff, Wharton Jones, Valentin, Wagner, 

 etc. It is now plainly demonstrated that the mammalia, includ- 

 ing man himself, spring, like birds and reptiles, from veritable 

 eggs." 



Here the question arises, What is an egg ? M. Quatrefages 

 answers, " Three spheres enclosed one in the other and con- 

 tained in a transparent membrane, constitute the germ." The 

 egg may differ in accessories, but "we always find in the vitel- 

 line membrane the vitellus, or yolk, enveloping the germinative 

 vesicle of Purldnye, which itself includes the germinating spot 

 of Wagner. The precise functions of each of these spheres is 

 far from being determined, but it is at least certain that the 

 vitellus is especially composed of organizable and nutritive 

 materials. In certain animals its alimentary provision is con- 

 siderable : a small part suffices for the constitution of the new 

 creature, which nourishes itself and grows at the expense of the 

 rest." The fish, for example, comes out of the egg completely 

 formed, and gradually assimilates the matter which his stomach 

 has enclosed. Among the viviparous animals the vitellus is 

 very small, and the embryo is nourished by materials obtained 

 elsewhere. The oviparous creatures lay their eggs, the vivipa- 



* This term is borrowed from the botanists. In Professor Henslow's valuable 

 Dictionary of Botanical Terms we read " caducous (caducus, ready to fall) when 

 a part falls off very early compared with other parts with which it is associated. 

 Thus the sepals of many poppies fall as soon as the flower begins to expand." 

 Caducous germs fall for the purpose of development. 



