STRUCTURE AND GROWTH OF DOMESTICATED ANIMALS. 647 
actly like these young eggs of the hen; so similar to them, that 
the most skilful observer is incapable of distinguishing 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 pecu- 
liarity: that the egg of a quadruped remains small, and while 
retaining these small dimensions undergoes of itself changes by 
which the germ is developed 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 
between 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 ani- 
mals. 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 structure characteristic of 
all ovarian eggs in their earliest condition. This is also the case 
With reptiles. Our little turtles lay eggs of considerable dimen- 
Sions 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 from the egg of the quadruped. And so it is 
with the fish, whatever be the kind of fish. I have. examined 
Many sharks and skates, as well as many of our salmon and trout 
and our various kinds of suckers and codfish, and I know that 
all these different kinds of fish produce similar ovarian eggs. 
Some of them lay them early, and lay eggs which are at once 
recognized as eggs, and others retain their eggs until the young 
are fully developed and they bring forth then, like the quadruped, 
living young; so that they exhibit within the limits of one and 
the same class differences similar to those which we observe among 
