26 Mary Blount. 



eggs. But each nucleus is attracted by the entire mass of cytoplasm 

 outside of the central fertilized area. Since the germinal area of 

 the pigeon's egg is shallow, the attractive force towards the central, 

 deeper part is less than that towards the periphery, and, therefore, 

 the sperm nuclei are drawn out to the periphery, i. e., into the 

 marginal periblast. But each nucleus, as it goes, leaves behind it 

 a fertilized path. This path, or radius, is then eliminated from the 

 attractive influence on any other nucleus. Another nucleus in its 

 original position near the first one referred to would pass out 

 along another radius, but since radii diverge toward the circum- 

 ference, the nuclei would take positions in the periblast further from 

 each other than they were in their original positions near the center. 

 This explains the more or less regular spacing of the nuclei around 

 the periphery. The application of this principle of attraction also 

 explains the position of the supernumerary nuclei in the central 

 periblast. If the cytoplasm near the surface was fertilized by other 

 migrating nuclei, the attractive influence of the remaining cytoplasm 

 would lead these nuclei into positions further below the surface. 

 Of course, I do not mean that the nuclei migrate successively. They 

 pass simultaneously each one along the resultant of the ' attractive 

 forces which act upon it. As they go, the influence of fertilization 

 emanates in all directions from each nucleus and so eliminates the 

 attraction from all directions, except the line of migration which the 

 nucleus is to follow. 



If these hypotheses are applied to the selachian egg, the positions 

 of the merocyte nuclei there are easily explained. The germinal 

 area of the selachian egg is proportionally much deeper than that 

 of the pigeon. It approaches the shape of a hemisphere with the 

 convex side toward the yolk. There is, therefore, a proportionally 

 greater attraction toward the deeper cytoplasm in the selachian egg 

 than in the pigeon egg, and the "merocyte" nuclei are found deep. 

 See Eiickert ('99), Figs. 37, 39 and others. Judging from descrip- 

 tions by Oppel and Ballowitz, I think this explanation will also serve 

 for the conditions in the reptilian egg. 



Polyspermy in Plants. — There remains yet to mention the case of 

 polyspermy in plants. Land ('07) found that the second male 



