REDUCTION IN UNICELLULAR FORMS 



279 



which the germ-nuclei unite (Fig. 139). Whether a reduction in the 

 number of chromosomes occurs in these cases was not determined.^ 



B 



C 



D 



E 



H 



Fig. 140. — Conjugation of Closterium. [Ki.EHAHN.] 

 A. Soon after union, four chromatophores. B. Chromatophores reduced to two, nuclei 

 distinct. C. Fusion of the nuclei. D. First cleavage of the zygote. E. Resulting 2-cell stage. 

 F. Second cleavage. G. Resulting stage, each cell bi-nucleate. H. Separation of the cells; 

 one of the nuclei in each enlarging to form the permanent nucleus, the other (probably repre- 

 senting a polar body) degenerating. 



^ Actinospharium forms one of the most extreine known cases of in-breeding; for the 

 gametes are siste?'-cells which immediately reunite after forming the polar bodies. The 

 general facts are as follows : The mother animal, containing very numerous nuclei, becomes 

 encysted, and a very large number of the nuclei degenerate. The body then segments into 



