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W. B. KIRKHAM AND H. S. BURR 



TABLE 1 



Shotving the relative number of eggs in the various stages of development at different 

 ■ periods of the oestrus cycle, as found in individual ovaries 



of such eggs in an ovary at any given time. This, however, v^^as 

 not the case, the number of Group III eggs found being rela- 

 tively close to the number of Group I eggs. 



Table I is compiled from a count of all the follicles in six 

 ovaries, representing each of the four periods. It shows the 

 relative number of eggs in each group present at the same time 

 in a given ovary. The count can only be an approximation, 

 owing to the occasional loss of a critical section and the fre- 

 quent difficulty in determining with accuracy whether or not 

 an egg was normal, but is sufficiently exact for this purpose. 



We were unable to obtain any stages that intervene between 

 the eggs of Group IV and those with the first polar spindle, so 

 we cannot say whether the nuclear membrance disappears before 

 or after the first appearance of the first polar spindle. With 

 regard to this spindle, however, there are a number of details 

 worthy of attention. It is short and broad, with well defined 

 fibers which do not come to a sharp focus (fig. 10). The possi- 

 bility of centrioles being present was mentioned by Coe ('08), 

 but these are apparently lacking in polar spindles of the albino 

 rat. The chromosomes are numerous, crowded, and never found 

 in a definite equatorial plate. Moat of the first polar spindles 

 seen are parallel to the surface of the egg, and this appears to 

 be the position in which the spindle waits for the stimulus that 

 leads to the formation of the first polar body (fig. 6 a) . When 

 this stimulus comes the spindle rotates on its long axis, coming 

 to lie more or less radially (fig. 6 b and 6 c) . 



