STRUCTURE OF DO^IESTICATED ANIMALS. 297 



ules inside, as the whole egg grows larger, burst and scatter 

 their contents throughout it; and the egg, from perfectly- 

 white, becomes slightly tinged with yellow, and finally grows 

 more and more opaque ; and, when the yolk has acquired its 

 full size and is ready to drop, it is really an opaque mass, 

 but consisting throughout of these minute granules. 



Now let us take the ovary of the rabbit, the guinea-pig, or 

 any other quadruped, and examine its contents, and we see 

 eggs exactly like these young eggs of the hen ; so similar to 

 them, that the most skilful observer is incapable of dis- 

 tinguishing the one from the other, — the egg of a rabbit 

 from that of a hen. Of course they do not remain in that 

 condition. There is this peculiarity : that the egg of a quad- 

 ruped remains small, and while retaining these small dimen- 

 sions undergoes of itself changes by which the germ is devel- 

 oped in time ; while, on the contrary, the egg of a bird grows 

 large ; even before it has its shell, its yolk becomes very large, 

 and it is surrounded by those auxiliary means of protection 

 necessary for an egg which is to be cast before the germ is 

 formed ; while the fecundated eggs of mammalia are not cast, 

 and the young undergo their development in the egg while 

 the latter is still retained by the parent. And so it has been 

 proved by Baer, that there is no difference whatsoever be- 

 tween so-called viviparous and oviparous animals, but that 

 all produce eggs which have the same identical structure, and 

 which differ from one another only by their various capacities, 

 by the various proportions which they attain, and by the 

 various ways in which the germ is developed in them. 



One more word to satisfy you that this is the case in all 

 animals. Eggs of the larger birds have been observed as I 

 have said, and it needs not to be repeated that in every species 

 in which the observation has been carried on, it has been 

 found that the ovarian egg, — that is, the egg prior to its 

 being laid, — has the small dimensions and the peculiar struc- 

 ture characteristic of all ovarian eggs in their earliest condi- 

 tion. This is also the case with reptiles. Our little turtles 

 lay eggs of considerable dimensions in comparison with their 

 size ; but examine their ovary, and you will find that there 

 are contained in that organ eggs of all possible dimensions, 

 as in the bird, and that when young these eggs do not differ 



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