THE MATURATION OF THE MOUSE EGG. 



263 



right angles to the radius of the egg, usually near the first polar 

 body. Centrioles, similar to those described above for the first 

 polar spindle, have frequently been observed in second polar 

 spindles, and in some cases a few radiating aster fibers have been 

 seen at the poles. In attempting to determine whether a given 

 polar spindle is first or second, the character of the chromatin 

 has always been found a positive guide. 



FIG. 5. Egg in Fallopian tube showing both polar bodies. Note spindle in first 

 polar body. The sperm head appears at left, the female pronucleus at right, in the 

 egg. X 1200. 



Mature eggs which are retained within the ovary, together with 

 such as are discharged and fail to be fertilized, degenerate with 

 the second polar spindle, as found by Rubaschkin ('05) in the 

 case of the guinea-pig egg. 



Second Polar Body (Figs. 5 and 6). Only one spermatozoon 

 enters an egg, and it carries in most, if not all of its tail, a fact 

 observed by Van der Stricht ('04) in the egg of V. noctnla. When 

 fertilized the egg at once forms its second polar body. This is 

 more or less nearly spherical, smaller than the first polar body, 

 and, as stated by Van der Stricht ('04) for V. noctnla, generally 



