MALE REPRODUCTIVE CELLS 



443 



some. In the Orthoptera he 

 was able to trace this chro- 

 mosome back to the sperma- 

 togonial rest stage. McClung 

 was the first to suggest a pos- 

 sible casual connection between 

 the dimorphism of sex and the 

 observed dimorphism of the sper- 

 matozoa. His conclusions were 

 drawn from his observations on 

 the maturation phenomena of 

 the Insecta, and the fact that sex 

 appears to be the only character 

 that divides the individuals of a 

 species into two approximately 

 equal groups. 



Recently there has been 

 great activity in the study of the 

 accessory chromosome and in a 

 search for this element in the 

 insects. It has been very thor- 

 oughly studied by Wilson ('05- 

 '06) in several of the Hemiptera 

 heteroptera (Anasa tristis, Pro- 

 tenor belfragei, Alydus pilosulus, 

 Harmostes reflexulus, Archimerus 

 calcarator, and Banasa calva). 

 Here the accessory chromosome 



is associated with a pair of small chromosomes which behave differ- 

 ently from the ordinary chromosomes (they remain condensed in the 

 growth stage) and are called by Wilson "microchromosomes." Miss 



Stevens ('06) has reported an 

 accessory chromosome in Aphro- 

 phora quadrangular is, one of 

 the Hemiptera homoptera (here 

 also associated with microchro- 

 mosomes) and in certain of the 

 Coleoptera. An odd chromo- 

 some very similar in behavior 

 to the accessory of orthoptera 

 FIG. 406. Three nurse cells on the basement has been reported by Berry ('02) 



FIG. 405. Fully developed spermatozoa of Raja 

 ocellata. The heads and middle pieces have 

 shortened and the sperm columns have become 

 compacted into regular bundles. Peculiar bod- 

 ies have developed on the distal end of each 

 nurse cell nucleus. X 1000. 



membrane of a sperm lobule of Raja ocellata. 

 The spermatozoa have been discharged from the 



lobule, x 1000. 





 m 



('05) in Scolopendra; however, 



