?8 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I39 



duct, the seminal vesicles, and the accessory glands now lie above the 

 intestine. Since the testes are not affected by the inversion, the long 

 vasa defer entia as in Culex (E) cross each other, but when the ducts 

 are united as in Aedes (D) a simple twist takes place at the junction 

 of the ducts. 



The testis of most insects consists of a number of individual tubes 

 in which the spermatozoa are formed as are the eggs in the ovarian 

 tubes, and, except in the apterygotes, the tubes of each testis are 

 enclosed in an investing sheath. The testes of the mosquito are 

 elongate, pear-shaped bodies (fig. 30 D,E,F, Tes) continuous with the 

 ducts. Each testis, however, appears in its entirety to be a single 

 testicular tube. The same is true of the testes in other Diptera. In the 

 narrowed upper end of each organ is a mass of undifferentiated cells ; 

 the rest of the lumen is filled with spermatocytes and spermatozoa 

 in various stages of development. The mature spermatozoa are ex- 

 tremely long and threadlike ; when liberated from the testis they 

 exhibit active undulatory movements. The spermatozoa are stored 

 in the seminal vesicles preliminary to mating, and the accessory glands 

 probably have a prostate function, giving the spermatozoa a liquid 

 medium in which they are discharged. 



The reproductive organs of the female mosquito, represented 

 diagrammatically at B of figure 30, include the parts characteristic of 

 the female organs of insects in general. These are a pair of ovaries 

 (Ov), the lateral oviducts (Odl) from the ovaries, and a median 

 common oviduct (Ode) with which the lateral ducts are joined. The 

 common duct opens by the primary genital aperture, or gonopore, into 

 a small pocket above the end of the eighth abdominal sternum. This 

 pocket, the genital chamber, or atrium, being a secondary inflection 

 of the body wall between the eighth and ninth abdominal segments, is 

 therefore not a part of the primary genital passage. The external 

 opening of the atrium may be designated the gonotreme (Gtr). Into 

 the dorsal wall of the atrium just behind the gonopore open the ducts 

 of the spermathecae (Spt), which are usually three in number, though 

 in Anopheles there is only a single spermatheca. Behind the 

 spermathecal openings arises an accessory gland (AcGld), the func- 

 tion of which is not known in the mosquito. In other insects accessory 

 glands usually secrete a cement for attaching the eggs to a support, 

 or a material to form an egg covering. 



The atrium serves as a copulatory pouch at the time of mating, and 

 the spermatozoa from the male are stored in the spermathecae. Then 

 when the eggs leave the oviduct they are received in the atrium and 



