f2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 139 



the ninth segment is a transverse basal arc (IX) usually containing a 

 small tergal sclerite. Beyond it is the tenth segment (X) bearing a 

 pair of lateral cerci (Cer) and the terminal anus (An). Ventrally is 

 a lobe known as the postgenital plate (pgpl) because the gonotreme 

 (H, Gtr), or opening of the genital atrium, is situated at its base 

 above the sternum of the eighth segment (VIII). The nature of the 

 postgenital plate is doubtful; it looks as if it should be the projecting 

 sternum of the ninth segment. On its base there is generally a trans- 

 verse fold known as the cozvl (K, a) because it is sometimes reflected 

 to form a hoodlike pocket. Surrounding the gonotreme above the 

 end of the eighth sternum is a sclerotized ring (b, c) named the sigma 

 by Christophers (1923). In figure K the ventral arc of the sigma (c) 

 is turned forward; normally it is directed posteriorly (J, c). The 

 sigma thus, as described by Christophers, resembles the lips of a half- 

 opened clasp purse, in which it is represented by the metal frame- 

 work of the purse. Some writers, however, without adducing specific 

 evidence, regard the dorsal arc of the sigma as the ninth sternum. 

 According to Christophers the whole structure is formed as a scleroti- 

 zation in the intersegmental membrane of the gonotreme. 



All parts of the female terminalia are subject to much variation, as 

 shown in comparative studies by Macfie and Ingram (1922), Christo- 

 phers (1923), Davis (1926), Gerry (1932), Gjullin (1937), Roth 

 (1946), Rees and Onishi (1951), and Hara (1957). The student, 

 however, will be somewhat confused by the different ways the parts 

 are represented and named. The drawings J and K on figure 27, taken 

 from Gerry, are composite diagrams showing all the parts that have 

 been described, but they probably do not present the exact structure 

 in any one species. 



The gonotreme surrounded by the sigma above the eighth abdominal 

 sternum leads into a small infolded pouch, the genital chamber, or 

 atrium. In its anterior wall is the female gonopore, which is the open- 

 ing of the median oviduct. Behind the gonopore the globular sperma- 

 thecae (one, two, or three in number) open through the dorsal wall of 

 the atrium, and into a posterior pouch of the dorsal wall, the caccus, 

 opens the single accessory gland, called the "mucus gland," but the 

 nature of its secretion is not known (fig. 30 B). 



INTERNAL ANATOMY 



A thorough study of the internal anatomy of the mosquito has not 

 been made, but the parts of principal interest will be the alimentary 

 canal and the reproductive organs. The muscular and tracheal systems 



