4 
of view. Ina few cases only (certain cannibal larve) a conspicuous series of 
hairs, forming a rudder-like expansion, springs from the median line posteriorly. 
On the eighth segment there are, on either side, a number of claw-like spines. 
Several small branched hairs also rise near the base of the siphon tube. 
Neither the spines nor the hairs appear to be of much importance in relation 
to classification, since they do not vary to any extent in the genera 
examined. The characters of the siphon tube are of importance, since this 
organ is subject to great variations in different genera and even in different 
species. The relative shortness or tenuity of the organ is an important 
character. In descriptions of larva the terms employed in describing this 
tube do not allow of accurate information being conveyed. I have therefore 
employed what I have termed the siphonic index. This is obtained by dividing 
the length by the greatest breadth of the tube. I have employed an eyepiece 
micrometer for the purpose of measurement. The figures given by the 
different genera have been very constant. 
Stegomyia sugens : - . é a 2 
; fasciata. ° 5 : p10} 
5 i 5 : 3 : 5k 1s) 
Desvotdea : : c : : oy 
Culex fatigans . é . : 5 21033 
35 ? : . . : 3 cei 
i impellens c 0 5 5 
sp fe C 2 . 0 & 
Melanoconion c . ‘ : . 9 IRS 
Tzniorhynchus tenax : : : og} 
ue N. SP. 4 : A ware 
In describing the siphon tube, it is desirable that a drawing accurately 
measured should be given, since the siphon tube is subject to the most 
extraordinary variations in size and shape. In tentorhynchus it is developed 
into a long and slender tube. In certain species not yet determined, the siphon 
tube is enormous. 
The ninth abdominal segment.—This very much modified segment lies, during 
life, so as to form an angle with the rest of the abdomen, and when the siphon 
tube is large has the appearance of an appendage rather than of an abdominal 
segment. It is cylindrical in shape, and covered dorsally and laterally by a 
single curved piece of chitin. The ventral surface of the segment is, for the 
most part, soft and membranous. Posteriorly is the opening of the anus and 
around this arranged symmetrically are the four amzal papzlle. In most 
larvee these papillz are of considerable size, reaching to about one-tenth of the 
body length. In others they are still larger and very conspicuous (Desvoidea). 
In some cases they are very small and rudimentary (cannibal larvee). The papillae 
