ROBERTSON: CHROMOSOME STUDIES IV. 281 



the split which is most apparent in the prophase figures 2 

 and 3. 



This is not the first time that such a phenomenon has been 

 described. Dehorne (1911) found the same to occur in the 

 somatic mitoses of Salamandra. In addition, I have reason to 

 believe that this phenomenon occurs in the chromosomes of the 

 first spermatocyte of the Tettigidse, while they are yet in the 

 daughter-cell stage resulting from the last spermatogonia! 

 division. There it seems that the chromosomes, before enter- 

 ing upon the stages of side-to-side pairing in synapsis, are in 

 reality definitely split along a longitudinal plane. Pairing 

 takes place evidently between members that are already made 

 up of two strands, and of course the four-part tetrad results. 



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