38 



THE EGGS OF MAMMALS 



mean ovum diameters are plotted against the mean follicle 

 diameters (see Figure 11) the resulting curves essentially 

 resemble those illustrated in previous figures, the full ovum 

 size being attained in follicles of type 5 which just precede 

 antrum formation. 



TABLE III 



Size of the Graafian Follicle at Various Stages of Its Life-History 

 (From Parkes, 1931) 



The data plotted in this manner give no indication of the 

 absolute rate of growth of ova though the relative growth rates 

 may be deduced from the rising segment of the curves drawn 

 to these data. These first segments are plotted in Figure 12, 

 wherein it might be deduced that the ferret ovum grows at the 

 most rapid rate, the pig ovum at the slowest rate, if com- 

 parable rates of follicular growth occur in the various species. 



If it be assumed that the various types of follicles de- 

 scribed by Pincus and Enzmann represent developments 

 occurring at equal time intervals then the lower curve of 

 Figure 11 may be taken as a representation of the growth 

 curve of the ovum. The sigmoid shape of this curve is in 

 fact reminiscent of general growth curves. It cannot be 

 taken as a true growth curve, however, until the time 

 necessary for the development of each type of follicle is 

 accurately known. Such information might very well be 

 obtained from ovaries subjected to x-irradiation and ex- 

 amined at various intervals after exposure. 



