62 HEREDITY AND SEX 



Herbst put the eggs of sphaerechinus into sea water 

 to which a httle valerianic acid had been added. This 

 is one of the many methods that Loeb has discovered 

 by which the egg may be induced to develop parthe- 

 nogenetically, i.e. without the intervention of the sper- 

 matozoon. After five minutes the eggs were removed to 

 pure sea water and the sperm of another species, stron- 

 gylocentrotus, was added. The sperm penetrated some 

 of the eggs. The eggs had already begun to undergo 

 the changes that lead to division of the cell — the sperm 

 entered ten minutes late. The egg proceeded to 

 divide, the sperm failed to keep pace, and fell behind. 

 Consequently, as shown in Fig. 34, the paternal 

 chromosomes fail to reach the poles when the nuclei 

 are re-formed there. The paternal chromosomes form 

 a nucleus of their own which comes to lie in one of the 

 two cells. In consequence one cell has a nucleus that 

 contains only the maternal chromosomes ; the other 

 cell contains two nuclei, one maternal and the other 

 paternal. In later development the paternal nucleus 

 becomes incorporated with the maternal nucleus of its 

 cell. There is produced an embryo which is maternal 

 on one side and hybrid on the other. Herbst found in 

 fact that half-and-half plutei were not rare under the 

 conditions of his experiment. 



This evidence is almost convincing, I think, in 

 favor of the view that the chromosomes are the es- 

 sential bearers of the hereditary qualities. For in 

 this case, whether the protoplasm of the embryo 

 comes from the egg or the sperm also, the fact re- 

 mains that the half with double nuclei is hybrid. 

 Even if the spermatozoon brought in some proto- 



