652 STRUCTURE AND GROWTH OF DOMESTICATED ANIMALS. 
well-kneaded yolk-mass very similar to what the primitive cell 
was, only that, instead of simple yolk-cells, it now consists of an 
innumerable quantity of little spheres which have resulted from 
the spontaneous division of the whole into successively multiplied 
halves. There is, however, this difference,—that on one side of 
the egg there is, when this process is completed, a larger number 
ig. 164. of these small balls or globules than Fig. 165. 
F 
pi ap 
5A the fact that the balls multiply more 4 
/ on one side than on the other. In \ 
quadrupeds this process of self-divi- 
sion pervades the whole yolk, so 
that in the centre and on the periphery, and on all sides, it is 
evenly divided, except that on one side the spheres are somewhat 
smaller and also somewhat more whitish. In the yolk of a hen 
Fig. 166, Fig. 167. 
a 
the process is widely different, and has been known only fora 
comparatively short time, for in the hen the process also takes 
place before the egg is laid. In order to examine it, therefore, 
Fig. 169. a hen must be killed and the egg must be 
observed during its passage through the ovi- 
duct, when on the surface of the yolk, and on 
the surface only, furrows are marked as if made 
with a nail. These furrows are multiplied cross- 
= wise, and then crosswise again, and this process 
is repeated until the whole surface is changed 
into these same globular bodies, already noticed 
in the rabbit and dog, but which in the hen extend only over 4 
small part of the surface of the yolk. Now this small part of the 
surface of the yolk is that white speck which is seen at once when 
you open the shell of an egg; and from it the chicken is developed. 
In fishes, there is still another process. Suppose we take the 
salmon. The first segmentation of the yolk consists in halving 
