Explanation of the Plate. 



DiaptoiuK!^ sp. Î- 



Fig. 1. — Lougitiidinal section of a testis : the lower end repre- 

 sents the formative /one and tlie np]^er end is tlie place where the vas 

 deferens takes its origin. Y TIT x Seibert = 120. 



Fig. 2. — The formative zone of the testis represented by fig. 1. 

 more highly magnified. A karyokinetic; figure at the right is drawn 

 here from the corresponding part of another animal. yVII x Sei- 

 bert = 850. 



Figs. 3~o. — Uepresent successive stages after the last division of 

 the cells in the formative zone. Y VIT x Seibert = 850. 



Fi(js. 6-8. — Cells from the formative zoiie. In figs. 6 & 7 the 

 eight chromosomes are still long and are difficult to count. In fig. 8 

 the chromosomes are much shortened in the cell on the right hand 

 side. 7 VII X Seibert = 850. 



Fi(is. 9, 10, cC- 11. — Show the first division of the sperm-mother 

 cell. Fig. 9 is drawn from a specimen killed with picro-acetic acid, 

 and coloured with hematoxylin. Three of the eight dumb-bell shaped 

 chromosomes are seen on this side and five others on the other side. 

 Figs. 10 and 11 are specimens killed with methyl -green-acetic acid. 

 In both figures the eight chromosomes lie on the periphery of a circle 

 and in both (^f them five elements lie on one side and the three others 

 on the other. All drawn by Seibert Y^^H ^md magnified 850 times. 



Figs. 12-16. — Sliow the second division of sperm-mother cells 

 immediately following the last division without an intermediate resting 



