ORIGIN AND TRANSFORMATION OF ANIMALS, 667 
transformations, general or partial, rapid or slow, and which 
only terminate with its life.” All animals likewise undergo 
transformations, which, considered radically, “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 phraseolog}’’, is in reality only nominal. Baer, in 
discovering the egg of the mammalia, M. Coste, in demon¬ 
strating 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 phy¬ 
siologists, Barry, Bernhardt, Bischoff, Wharton Jones, Va¬ 
lentin, Wagner, &c. It is now plainly demonstrated that 
the mammalia, including 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 vitelline membrane the vitellus, or yolk, enveloping the 
germinative vesicle of Purkinje, which itself includes the germi¬ 
nating 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 considerable; a small part suffices for the con¬ 
stitution 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 assi¬ 
milates the matter which his stomach has enclosed. Amono; 
the viviparous animals the vitellus is very small, and the 
embryo is nourished by materials obtained elsewhere. The 
oviparous creatures lay their eggs, the viviparous retain them 
for internal development; but birds, worms, reptiles, and 
men, all are hatched. 
The viviparous, and many of the oviparous tribes, resemble 
their parents as soon as they have passed the foetal stage. 
* 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. 
