HEEEDITY 



all other cells of the prothallus are already 

 in tlie reduced condition without any matura- 

 tion divisions. The result of their union in 

 pairs, at fertilization, is the formation of 2 N 

 combinations that germinate into fern-plants. 

 Similarly in the case of a male animal which 





Fig. 8. — Diagram showing the chromosome number in the 

 spermatogenesis of ordinary animals (upper Une) and of the 

 wasp (lower line). 



has developed from a reduced but unfertilized 

 egg, no reduction occurs at the formation of 

 its sperm-cells. In an ordinary male animal, 

 one which is in the double or 2N state, the 

 development of the sperms is attended by re- 

 duction to the N condition. In this process 

 there occur two cell-divisions producing from 

 each initial cell four sperms. See Fig, 5, and 



24 



