110 CHARLES PACKARD 



The germinal vesicle breaks down as a rule, within a few 

 minutes after insemination, even though the alveolar layer is 

 still present. The egg centrosome divides normally, the daughter 

 centrosomes migrating to the opposite sides of the group of chrom- 

 osomes which lie free in the protoplasm without any definite ar- 

 rangement. If the alveolar layer has been extruded the spindle 

 usually moves to the surface where it develops normally in many 

 cases. In such instances the chromosomes are not at all affected, 

 but split into the normal crosses and rings with great precision. 

 The achromatic figure also appears to be normal. When the 

 alveolar layer is not extruded at once, and, in some cases, even 

 when it is, the whole first polar figure remains near the center 

 of the egg. Judging from the scarcity of extruded polar bodies, it 

 is probable that the polar body is not often extruded. 



There are, however, several marked departures from the course 

 outlines above. Figure 31 shows a condition found in several 

 eggs. There is but one centrosome and no real aster. The 

 spindle fibers are normal and attached to the chromatin masses. 

 No normal chromosomes are present, the chromatin remaining 

 either as a long narrow thread, or as irregular, homogeneous 

 masses. In each instance it is in two distinct groups separated 

 by a varying distance. The size of the chromatin thread indi- 

 cates that splitting has not occurred in the right hand group. 

 In the other group the chromatin is in very irregular masses of 

 unequal size. Figure 32 is a later stage of the same condition. 

 In this egg there is a normal sperm head and cone already revolved, 

 but the sperm aster is not apparent. Some of the chromosomes 

 are fairly normal, while others are mere masses of chromatin. 

 The separation of .the groups and of the spindle fibers attached to 

 them is a curious phenomenon. In some instances both polar 

 bodies are given off, but in many cases none at all are extruded. 



During this time the sperm heads have developed up to the 

 vesicular stage, as has been mentioned above. Their further 

 development may proceed along different paths. In some in- 

 stances the karyomeres apparently break down and fuse together, 

 taking the form of fine spireme, or even breaking up into chrom- 

 osomes. If several sperm heads enter there are at least as many 



