60 J. T. PATTERSON. 



has eight clear chromosomes. In the upper or first polar body 

 group eight are also present, but they are somewhat massed 

 together. These observations indicate that the first maturation 

 division results in separating the two components of each bivalent 

 chromosome, so that the first polar body receives eight whole 

 chromosomes, as does likewise the second oocyte. 



SECOND MATURATION. 



The second maturation occurs soon after the first is completed. 

 The chromatin does not reorganize a nucleus. The first polar 

 body chromatin likewise divides without forming a nucleus. 



The second maturation and the division of the polar body 

 may occur simultaneously (Fig. 12), or the polar body division 

 may either precede (Fig. n) or follow (Fig. 2) the second 

 maturation division. There is therefore no close correlation 

 between the divisions of these two groups of chromosomes. 



In Fig. 1 1 the late anaphase stage of the first polar body 

 division shows eight chromosomes at each end of the spindle. 

 The group of chromosomes lying just below also has eight. 

 This is the second oocyte group. In Fig. 12 the two division 

 figures are in the late anaphase stage. At the upper end of the 

 polar body spindle (above) six chromatin masses are present, 

 while at the lower end there are eight. The second oocyte 

 spindle has seven above and eight below. If these two divisions 

 are equational in character, we should expect to find eight 

 chromosomes in each group. Our failure to do so is probably 

 due to the fact that one or more chromosomes in a group may 

 be hidden by some of the other chromosomes. 



FERTILIZATION. 



As already stated the egg is inseminated by a single sperm, 

 which lies in the lower half of the newly laid egg. Although 

 the entire sperm enters the egg, only the sperm head becomes 

 transformed into the male pronucleus, the formation of which 

 is completed by the close of maturation. 



Of the four groups of chromosomes referred to in. connection 

 with Fig. 12, the three lying nearest to the surface of the egg 

 represent the three polar bodies, while the one lying toward the 



