THE DOG S EGG 



83 



domestic utility; and wants the shell, which 

 would not only be useless to an animal incubated 

 within the body of its parent, but would cut it off 

 from access to the source of that nutriment which 

 the young creature requires, but which the minute 

 egg of the mammal does not contain within 

 Itself. 



FIG. 13. A. Egg of the Dog, with the vitelline mem- 

 brane burst, so as to give exit to the yelk, the germinal vesicle 

 (a\ and its included spot (b). B. C. D. E. F. Successive 

 changes of the yelk indicated in the text. After Bischoff. 



The Dog's egg is, in fact, a little spheroidal bag 

 (Fig. 13), formed of a delicate transparent mem- 

 brane called the vitelline membrane, and about T ^ th 

 to T^-Q-th of an inch in diameter. It contains a 



