THE MORPHOLOGY OF FERTILIZATION 79 



the supernumerary sperm nuclei move away from the 

 center as though repelled and accumulate in the periph- 

 eral periblast. Here they undergo division and pro- 

 duce cell areas in the periblast, which are a conspicuous 





FIG. 12. Part of a horizontal section of the germinal disk of a 

 pigeon's egg freed from the ovary, but not yet in the oviduct. First 

 maturation spindle (M.S. i) cut transversely in the center; sperm nuclei 

 (Sp.N.) surrounding it (after E. H. Harper). 



feature' of the development up to about the thirty- 

 two-celled stage, at which time, according to Miss 

 Blount. they begin to degenerate, and soon entirely 

 disappear. The segmentation nucleus in this case is 

 thus formed of the union of the egg nucleus and a single 

 sperm nucleus in the usual way, and all nuclei of the 

 embryo are derived from this by karyokinetic division. 

 In Selachia the phenomena are similar, but Riickert 

 maintains that the supernumerary sperm nuclei persist 



