l6o M. \V. BLACK MAN. 



EXPLANATION' OF PLATE II. 



Figs. 16-18 represent the chromosomes of the small type of spermatocyte in a 

 similar stage. 



Figs. 19 and 20 represent the chromosomes of the two second spermatocytes, 

 derived from one primary spermatocyte. The individual chromosomes are arranged 

 so as to correspond in position to the parent chromosomes as seen in the other 

 figures. As will be seen, in one cell the accessory chromosome is not present, it 

 being distributed to only half of the secondary spermatocytes. 



