io Vertebrate Embryology 



A mass of frog's spawn may be compared 

 to a number of hen's eggs which have been 

 carefully broken into a dish, so that the yolks 

 are all unbroken. The yolks of the hen's eggs 

 correspond to the true eggs of the frog's spawn, 

 and the white of the hen's egg to the jelly 

 mass of the spawn. The white of the hen's 

 egg, however, serves as food for the develop- 

 ing chick, while the jelly of the spawn probably 

 serves no such purpose. 



Maturation of the Egg 



As a rule, before an egg may begin its de- 

 velopment, it must be fertilized, and before it 

 can be fertilized it must undergo a process of 

 ripening or maturation. The details of this 

 maturation vary in different eggs, but the es- 

 sential processes are about the same in all. 



As has been stated above, the egg of the 

 frog, when just set free from the ovary, con- 

 tains a very large nucleus. It is the nucleus 

 that is chiefly concerned in the maturation 

 changes, and the first change that is noticed is 

 a shrinkage of this large nucleus and a loss of 

 the nuclear membrane. After passing through 

 other changes, a description of which cannot 

 be given here, the nucleus divides into two 



