DAVIS : SPERMATOGENESIS. 



65 



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The testes, which are so 

 closely apposed as to pre- 

 sent the appearance of a 

 single organ on superficial 

 examination, lie in the dor- 

 sal part of the fourth to the 

 sixth abdominal segments. 

 Each testis is composed of 

 a number of elongate, cy- 

 lindrical follicles (appar- 

 ently corresponding to ova- 

 rioles), tapering somewhat 

 at either end and lying 

 approximately parallel to 

 each other. However, in 

 adults after the spermato- 

 zoa have partially matured 

 the proximal ends of the 

 follicles become much con- 

 stricted. Each follicle is 

 connected at its anterior 

 (proximal) end with the 

 vas deferens. The follicles 

 of each testis are inclosed 

 in a delicate connective- 

 tissue membrane, which 

 usually contains an orange 

 colored pigment. 



In a longitudinal section 

 each follicle (Fig. A) is 

 seen to be filled with a 

 mass of germ cells in suc- 

 cessively older stages from 

 the distal to the proximal 

 end. At the distal end 

 there is always a single 

 large apical cell around 

 which the primary sper- 

 matogonia are arranged in 

 a single layer. Surround- 

 ing the primary spermato- 

 gonia are large numbers 



