NO. 14 INSECT ABDOMEN SNODGRASS 67 



prolongations (a) from the epithelial walls (Epth) of the gonad. 

 The testicular cysts of other insects are said to be formed of cells 

 descended from the spermatogonia. 



The simple shape of the gonads is most fully carried over into the 

 adult stage in Anurida, in which the ovaries and testes, though they 

 may increase greatly in size from the immature stages, retain for the 

 most part an undivided saclike form (fig. 23 A, B). The germinal 

 area of Anurida, as described by Lecaillon (1902) and by Imms 

 ( 1906), lies in the dorsal wall of the gonad (D, Grm). In the male, 

 Imms says, " the germinal tissue is in the form of a mass or ridge, 

 situated at about the middle of the length of the testis ", in the female 

 it forms in each ovary " a protruding ridge lying in the region of the 

 third and fourth abdominal segments." In Podura, according to 

 Willem (1900), the adult gonads are voluminous organs occupying 

 the abdomen and the last two segments of the thorax. Each gonad is 

 an irregular sac (F) with its mesal wall produced into five large 

 pouches separated by deep incisions, but the germarial zone of the 

 testis extends through the entire length of the dorsal wall of the 

 organ, both on the undivided lateral part and on the mesal pouches. 



In the Entomobryidae. as shown by Willem (1900), the immature 

 gonads are simple fusiform sacs as in the young of Poduridae, but in 

 each sex the germarium is localized in the apex of the organ, evi- 

 dently a secondary condition, Willem contends. As development pro- 

 ceeds, however, each gonad grows anteriorly and posteriorly beyond 

 the germinal zone in each direction, with the result that in the defini- 

 tive organ, the germarium is a restricted area of the lateral wall of 

 the gonad near the posterior end of the latter (fig. 23 G, Grm). In 

 this family the gonad becomes two-branched by the development of a 

 long mesal lobe opposite the germarium. The gonads of Neelidae and 

 Sminthuridae are undivided tubes, but each tube is bent upon itself 

 because of the limited space in the globular abdomen. According to 

 Lecaillon (1902) the germinal zone in the male of these families is 

 restricted to the apex of the testis; in the female of Sminthurns, 

 Willem says, the germinal region of the ovary lies ventrally in the 

 outer wall of the middle part of the tube, but much nearer the anterior 

 end of the latter than in Poduridae and Entomobryidae. 



From the above review of the structure and development of the 

 coUembolan gonads it is evident that the organs, beginning with a 

 generalized condition, have followed a line of specialization confined 

 to the Collembola. The primitive gonadial sac. as represented by the 

 testis of Poduridae, probably had a germarial band in its dorsal wall. 

 The localization of the germarium in the apex of the gonad in other 



