106 



THE EGGS OF MAMMALS 



have a very large single cell, beside which lie a number of 

 very small ''cells" comparable in appearance to polar bodies. 

 Very often this group of ''polar bodies" resembles an ir- 

 regular indented cytoplasmic mass, and I have actually seen 

 it formed as such a mass budded or divided off from the 

 main body of the cell. This represents the extreme of 

 irregularity observed. 



The foregoing account has been given irrespective of the 

 age of the ova figured. It remains for us to ascertain if any 

 relation does exist between the age of the ova cultured and 

 the nature of their development. Before proceeding to a 

 detailed inquiry, however, it must be pointed out that the 

 various types of ova described and figured in the photo- 

 graphs have been observed in ova of all ages so that no 

 absolute correlation exists. Ova have been considered as 

 segmenting regularly only when the cells of the two, four, 

 eight and sixteen cell stages have been of equal size, or 

 when one could obviously trace the regular descent of the 

 cells in ova exhibiting intermediate stages. In the cases of 

 ova exhibiting many cells only those showing clear cell 

 outlines and cells of equal size have been classified as 

 "regular." 



TABLE XVIII 



Effect of Age of Ova when Removed from Doe on Subsequent 

 Regularity of Division in Vitro. (From Pincus, 1930) 



In Table XVIII the data are collected into three groups 

 as follows: (1) Ova recovered when practically all were in 

 the cumulus mass; (2) ova separating out of cumulus mass 

 and not yet covered with albumen ; (3) ova covered with the 

 albumen deposit. It is obvious from these data that the 



