644 STRUCTURE AND GROWTH OF DOMESTICATED ANIMALS. 
young German physiologists, Pander and D'Alton, under the 
guidance of Professor Déllinger, began that study, and, in order 
to ascertain how the chick is formed, —not how the chick grows 
in the egg, but how it is formed during the first hours after the 
sitting of the hen upon the egg has begun, — they opened three 
thousand eggs. Now, why is it that we have not yet such knowl- 
edge of the horse? Because there are not three thousand mares 
to be sacrificed to study their development; and unless some 
means are found by which something of the kind can be done, we 
cannot have the beginning of the history of that one animal; 
unless, perhaps, with the greater knowledge we now possess and 
long acquired skill, a smaller number of individuals may suffice ; 
but not until hundreds and hundreds of animals are sacrificed for 
that purpose, under proper conditions, can we have the first fact 
concerning their history. And if you find in physiological text- 
books this subject treated as if it were entirely known, it is simply 
because the data in reference to the animals, the physiology of 
which is given in our text-books, are borrowed from the four ani- 
mals carefully studied by Bischoff, and not from any particular 
knowledge obtained from the domesticated animals themselves. 
When, in our human physiology the embryology of the human 
race is presented, it is largely illustrated by conditions which have 
been studied from the rabbit, the dog, the guinea-pig and the 
roebuck. Direct observations are so few that they are hardly 
worth mentioning. A few cases of suicide have furnished the 
only information which is on record concerning the first condition 
of the human being. 
And now I propose to show you what an egg is, and then to 
satisfy you that all animals produce such parts as deserve the 
name of egg. 
A hen’s egg, surrounded by its shell, which is calcareous, is 
lined on the interior by a double membrane. A skin extends over 
the whole internal surface, and that skin is double; and in one 
part of the shell it recedes from the shell and leaves an open 
space, which is the air-chamber of the egg. These are only pro- 
tections of the egg, and are formed last upon it. In the interior 
of the egg we have a round ball of yolk which is suspended in the 
egg by two cords of somewhat harder albumen than that which 
surrounds the yolk. These two cords keep the yolk so suspended 
in the egg that whatever position you give the egg, certain 
