68 MOSQUITOES OF NORTH AMERICA 
certain extent at least these modifications are correlated to the mode of ovi- 
position. Thus in Culex, Culiseta, Mansonia and Uranotenia, 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 Psorophora, and most species of Aédes, which deposit 
their eggs singly, the abdomen tapers towards the tip and the cerci are long, 
slender and exserted. 
In Psorophora 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 Aédes 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 Aédes, 
continuously chitinized and clothed with 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 sete 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 sete 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 
Carrollia and in Wyeomyia codiocampa the abdomen is strongly compressed. 
In the Sabethini the abdomen is usually subcylindrical and blunt at the tip, and 
