OVULATION IN MAMMALS. 249 



belonging to eggs themselves degenerating within the ovaries, 

 others in the process of early cleavage in the Fallopian tubes — 

 make it practically certain that in the case of such mouse eggs 

 as have reached or passed the stage when the second maturation 

 spindle is formed, and yet show no trace of the first polar body, 

 this body has broken up and disappeared; in all instances of 

 such degeneration the chromatin granules lose their distinctive 

 staining qualities some time before the final dissolution of the 

 polar body cytoplasm. 



The observations on rats were limited to two adult white fe- 

 males. These animals were kept in a large cage with males and 

 other females until they -showed signs of advanced pregnancy. 

 They were then isolated in separate cages, and a close watch was 

 kept for the appearance of the litters. As soon as found, the 

 young rats were taken from their mothers, and then the latter 

 were killed, one twenty-four, the other forty-eight hours later; 

 it having been previously determined that the white rat, like the' 

 white mouse, during the warm months of the year is usually in 

 heat directly after giving birth to a litter. When the bodies of 

 these animals were opened, characteristic corpora lutea were vis- 

 ible on all the ovaries, and after the ovaries and Fallopian tubes 

 had been sectioned and stained, eight tube eggs were found in 

 one animal, and five in the other. These eggs have exactly the 

 appearance of eggs obtained from female white rats which have 

 been allowed to pair and then are killed just before fertilization 

 can take place; the zona pellucida in all cases is well preserved, 

 all of the eggs possess second polar spindles, while a majority 

 show no trace of the first polar body, it probably having previ- 

 ously degenerated. 



The points to be emphasized in these researches are three in 

 number: 



1. Virgin white mice mature eggs and discharge them from 

 their ovaries at practically the same age as their sisters who have 

 been allowed to pair, and such eggs show no differences from 

 other unfertilized eggs, 



2. Adult female white rats during the active breeding season 

 ovulate regularly, immediately after giving birth to a litter, 

 whether pairing is or is not allowed to take place. 



