MECHANISM IN SEOEEGATION 



47 



the ordinary mitotic process. The cells then pass into the 

 synaptic stage (Fig. 20, a-d). As the chromosomes begin 



a 





g 



Fig. 19. — Thin-thread stage of Tomopferis spermatocyte, a-d; tetrads, e; first sperma- 

 tocyte division, /-/; second spermatocyte division,./-/. (After Schreiner). 



to emerge as thin threads, it is found in Batracoseps that 

 their ends are all pointed towards one pole (Fig. 20, d)- 

 This is the same pole as that towards which the two ends 



