Eugene Howard Harper ^75 



of fusion^ and also apparent disintegration of some. These appearances 

 may arise from pluripolar spindles, which have not j-et been found in 

 the pigeon, but which are undoubtedly to be found here as in the 

 selachian. Other evidences of attempts at mitosis are to be found. Often 

 a spireme is found of irregular appearance, indirect division proceeding 

 no farther. There were no accessory cleavage furrows recognized at this 

 stage. 



Are the nuclei incorporated into the cleavage area? There is no 

 affirmative evidence on this point. On the contrary, there is a distinct 

 separation between cleavage cells and yolk underneath the blastoderm, 

 the marginal cells having complete cell boundaries. No nuclei at all 

 resembling the yolk nuclei have been found within the cleavage area. 

 The cleavage nuclei are distinct in appearance and are not easily to be 

 confused with the nuclei in the yolk. 



The only evidence obtained having a possible bearing on the fate of 

 the yolk nuclei is the occurrence of great numbers of peculiar refractive 

 bodies closely associated with the nuclei in the large nuclear nests. These 

 todies resemble the disintegrating nucleoli of the late ovarian egg. In a 

 nest such as shown in Fig. 38 there are large masses of this refractive 

 substance made up of clusters of vesicles. There are also isolated rod-like 

 bodies of the same material. May these not indicate that there is a 

 constant reduction in the amount of chromatin material due to " karyo- 

 litic" action? The yolk nuclei are very numerous at this stage, and 

 form a fringe around the blastoderm, but do not go far out into the 

 yolk. Their numbers at the start, if augmented by division followed by 

 migration, ought soon to fill the yolk, as it would seem. On the con- 

 trary, the margin of the blastoderm seems to be the only region occupied 

 by them. The liquefied products of this karyolitic action are doubtless 

 absorbed by the embryonic cells. The refractive bodies are probably 

 material in process of dissolution, as is apparent in the case of the 

 nucleoli of the late ovarian egg. 



Polyspermy ix Other Eggs. 



The term physiological polyspermy has been applied to all cases where 

 more than one spermatozoon normally enters the egg. The fate of the 

 supernumerary sperms is by no means the same in the different groups 

 in which the phenomena occur. Hitherto, in the elasmobranchs alone 

 has their persistence to form yolk nuclei or " merocytes " been observed. 

 The nearest approach to this condition was found by Oppel, 92, in the 

 reptilia, where the sperm nuclei though present in large numbers, divided 

 slowly and karyolitically, and soon degenerated. The evidence in the 

 ■case of the reptilia is, however, fragmentary. 



