68 MOSQUITOES OF NOETH AMERICA 



certain extent at least these modifications are correlated to the mode of ovi- 

 position. Thus in Culex, Culiseta, Mansonia and U ranotcenia, which lay their 

 eggs in a raft, the tip of the abdomen is blunt and the cerci are small and broad 

 and not promiment. In Psoropliora, and most species of A'edes, which deposit 

 their eggs singly, the abdomen tapers towards the tip and the cerci are long, 

 slender and exserted. 



In Psoropliora the eighth segment is flexible and completely retractile within 

 the seventh. Basally on the eighth segment there is a broad area of membranous 

 tissue ; outwardly are the tergum and sternum and these are also membranous 

 in character but differentiated in structure by the presence of numerous minute 

 transverse strips of chitin. Internally the two plates are supported by two pairs 

 of slender chitinous rods and these probably also form part of the mechanism 

 for retracting the segment. The sternite is broadened posteriorly and projects 

 considerably beyond the tergite, thus forming a ventral support for the greatly 

 reduced ninth segment. The eighth segment when fully protruded is longer 

 than the preceding one. In most species of Aedes the eighth segment is partly 

 retractile, having a broad basal membrane, but this is not as extensive as in the 

 forms just described. The tergal and sternal plates are, however, in Aedes, 

 continuously chitinized and clothed Math hairs and scales. 



In the females of Deinocerites and Dinomimetes the abdomen is long, some- 

 what compressed, and slightly tapered towards the tip; the eighth segment is 

 peculiarly modified. The tergite of the eighth segment presents nothing un- 

 usual but the sternite is larger, compressed, and produced posteriorly, the apical 

 portion heavily chitinized. In Dinomimetes epitedeus and Deinocerites pseudes 

 the sternite is much produced in the form of two rounded lateral lobes, their 

 upper portions most prominent ; the margins of the lobes are closely beset with 

 coarse setse inserted in tubercles. In Deinocerites cancer and related forms the 

 lobes of the eighth sternite are roughly quadrate and very heavily chitinized, 

 with the lower angle somewhat produced ; upon this angle and along the lower 

 margin are a series of tubercles bearing coarse setse which give the margin a 

 serrate effect. In this last-described type of Deinocerites the cerci reach an un- 

 usual development. They are large, conical, heavily chitinized, and have in- 

 serted at their apices a pair of long, slender flattened appendages. The gona- 

 pophyses are inconspicuous in these forms. The shape of the sternal lobes and 

 of the cerci differs in the different species. In Deinocerites pseudes and Dino- 

 mimetes epitedeus the cerci are, as in other mosquitoes, without terminal ap- 

 pendages ; they are, however, rather large, leaf -like and heavily chitinized. In 

 these two species the gonapophyses are well developed, heavily chitinized and 

 setose. 



The eighth abdominal segment of the female Mansonia titillans is remarkable 

 in that it is completely retractile within the seventh while its tergite is mem- 

 branous and bears at its apical margin a row of stout chitinous hooks. In many 

 forms the abdomen is more or less depressed, particularly towards the base. In 

 Ca/rroUia and in Wyeomyia codiocampa the abdomen is strongly compressed. 

 In the Sabethini the abdomen is usually subcylindrical and blunt at the tip, and 



