30 Fertilization and Early Development of Pigeon's Egg 



the sperm nuclei exhibit normally a repulsion for each other due to ihe 

 presence and activity in some way of their accompanying sphere sub- 

 stance. The aibsence or feebler development of the sphere substance in 

 the egg nucleus accounts for the mutual attraction displayed by the male 

 and female pronuclei. Moreover, the mutual repulsion of sperm nuclei 

 disappears with the change of their environment from the germinal disc 

 to the yolk as it disappears in the abnormal environment of nicotin- 

 ized eggs. Hence conjugation of nuclei occurs in the yolk, giving rise 

 to giant nuclei, pluripolar spindles and progressively increasing irregu- 

 larity of division ending in amitosis. 



As to the adaptation of polyspermy to the large meroblastic egg, 

 Boveri suggested that polyspermy was necessary in the case of the large 

 egg to insure certainty of fertilization. Riickert maintains that the 

 force of this argument is weakened by the fact that the region where 

 the sperms may enter is very limited and is in close proximity to the 

 egg nucleus. Sobotta accepted the above view of Boveri and also argued 

 that the size of the egg was the factor which prevented multiple coniu- 

 gation with the egg nucleus, since the sperms could never in so large 

 an egg enter at exactly the same time. Hence they would always be 

 unequal in development, and the largest would become the male pro- 

 nucleus. Eiiekert points out the inconsistency of maintaining that the 

 size of the egg requires the entrance of many sperms to insure fertili- 

 zation, and that the size of the egg is also what prevents multiple fertili- 

 zation. Eiiekert believes that the mutual repulsion of sperm nuclei is 

 at least to be regarded as a fact in the selachian egg, if not proved true 

 for all monospermic eggs. He thinks it improbable that the sperm- 

 nuclei have a normal function in the embryonic development, and leaves 

 open the question of a possible second generation of nuclei arising from 

 the cleavage cells in later stages homologous with the periblast of teleosts. 



As to the cause of migration of the accessory nuclei into the yolk, 

 Eiiekert adduces his theory of repulsion, holding that the sperm nuclei 

 are driven from the germinal disc by the advancing cleavage nuclei, 

 owing to their superior power of repulsion. If the observations upon 

 the pigeon in this regard prove anything, it is that the sperm nuclei 

 migrate so early to the periphery of the germinal disc that it is difficult 

 to believe they do this under the influence of the cleavage nuclei. As 

 pointed out, they are found in the accessory cleavage region, far removed 

 from the affected area in the center of the disc, which seems to be the 

 sphere of influence of the cleavage nuclei, as early as the formation of the 

 first cleavage furrow. Moreover, they are nearly absent from the inter- 

 mediate region at this time. This seems to point to the independent 



