Carpenter et al.: Mosquitoes of Southern U. S. 47 



thorax in the genus Bironella. Located antero-dorsally on the thorax is a pair 

 of transparent retractile notched organs of Nuttall and Shipley. When ex- 

 tended, these organs make contact with the surface film and probably help to 

 support the larva. According to some authors these organs may prevent the 

 thorax from rotating with the head before and after feeding. 



ABDOMEN. (Figs. 21, 22). — The structures of most taxonomic importance 

 on abdominal segments I to VII are the dorsal anterior submedian hair (0), 

 pahnate hair (1), antepalmate hair (2), sublateral hairs (3-5), lateral hairs 

 (6-8), the main tergal plate and the median accessory tergal plate. Segment 

 VIII bears the spiracular structures postero-dorsally (a siphon is lacking), the 

 pecten laterally, and hairs as illustrated (Fig. 22A, B). The pecten present on 

 each side of segment VIII, is a sessile, sclerotized plate, bearing both long 

 and short teeth, and according to Christophers (40) is homologous with the 

 pecten of Culicine larvae. Segment IX (^anal segment) is partially ringed by 

 a sclerotized dorsal plate which has toward its posterior margin a lateral hair, 

 usually single. From the dorso-apical angle of the anal segment arises the dorsal 

 brush composed of the upper and lower caudal hairs. The ventro-apical margin 

 has a fan-shaped group of hairs known as the ventral brush. Four tapering 

 papilliform processes, the anal gills, are borne posteriorly. 



Egg Characters 



The eggs of mosquitoes are composed of three distinct layers: The delicate 

 vitelline membrane surrounding the yolk; the endochorion, a more or less 

 heavily sclerotized outer shell; and the exochorion, a thin hyaline layer covering 

 the endochorion and patterned with small protuberances and reticulations. The 

 endo- and exochorion together make up the chorion. The anterior pole of the 

 egg bears the micropylar apparatus, which consists of a small, rosette-shaped 

 membrane and a ring of exochorial bosses surrounding a minute opening, the 

 micropyle. The micropyle permits entrance of a sperm cell from the sperma- 

 thecae of the female during oviposition. 



The eggs of Culicine mosquitoes are usually elongate-oval in sagittal 

 section and circular in cross section. The larger, anterior end, containing the 

 head of the developing embryo, is somewhat rounded, while the posterior end 

 is bluntly pointed. The eggs are laid singly by some species while certain others 

 lay them in rafts (Fig. 23). The shape of the individual egg is rather charac- 

 teristic for various genera; the nature of the markings of the exochorion and 

 the manner in which the eggs are laid are also useful in classification. 



The eggs of Anopheline mosquitoes are usually boat-shaped, flattened or 

 slightly concave dorsally, and decidedly convex ventrally (Fig. 23C, D) . The 

 larger, anterior end is somewhat rounded, while the slightly narrower posterior 

 end is more or less bluntly pointed. The exochorion is modified to form a 

 projecting jrill, which partially or entirely surrounds the upper portion, and a 

 pair of air-filled lateral floats. The character of these structures, together with 

 the bosses and reticulations of the exochorion, are of considerable value in 

 separating allied species and races in some parts of the world. 



