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. 1 



Fig. 140. Conjugation of Closterium. [K.LEBAHN.] 



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

 distinct. C. Fusion of the nuclei. D. First cleavage of the zygote. . 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. 



1 Actinosphatrium forms one of the most extreme known cases of in-breeding; for the 

 gametes are sister-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 



