MODIFICATIONS OF MOUTH-PAKTS 49 



of successively older ages to pupation and the achievement of the definitive 

 imaginal condition of these parts, it is certain that the parts marked respect- 

 ively imaginal mandible, imaginal maxillae, and imaginal labium, lying respect- 

 ively in the larval mandibles, maxillaa, and labium (with homologies firmly 

 based on ontogenic basis), do develop into those definitive imaginal parts named 

 mandibles, maxillae, and labium. . . . Fig. 2, a horizontal, frontal section 

 through the head of a Simulium larva, shows also the forming imaginal maxilla 

 and mandibles within corresponding larval parts/' 



Wesche has found that abnormal male Culicidae occur with all the trophi 

 present, as in the females, although in these cases the maxillse and mandibles did 

 not extend to the tip of the proboscis. Such males, to conclude from Wesche's 

 work, appear to be not uncommon. Examining a number of males of different 

 species, he found an abnormal Anopheles and also a male Culex pipiens with all 

 the parts present. 



It would seem that the mandibles and maxillse may be absent in the female of 

 certain species which do not suck blood. Such appears to be the case with the 

 female of Harpagomyia splendens, recently described by De Meijere. This 

 curious Javan species feeds upon honey which it obliges the ant, Cremastogaster 

 difformis, to disgorge. In this mosquito the hypopharynx is free, as usual, but 

 appears to lack the salivary duct. It is interesting to note that early in the 

 pupal stage both mandibles and maxillae can be readily seen in the developing 

 imago. These gradually retrograde, until, by the end of the pupal period, they 

 have become wholly atrophied, just as has been shown to occur in the develop- 

 ment of the males of the blood-sucking forms. 



While the external appearance of the proboscis is frequently described, we 

 know practically nothing of the modifications of structure in the different species 

 or genera — Wesche states that in Anopheles the mandibles are serrated at the 

 tip. The sheath of the proboscis shows much variation in length and diameter 

 in the different species and it is frequently expanded towards the apex. The 

 labellae also show much difference in shape and in details of structure but these 

 need not be described. In Megarhinus the sheath is unusually rigid, tapering, 

 becoming very slender at the tip, and the labellas are narrow and much elongated. 

 In this genus, in which both sexes feed wholly upon the honey of flowers, the 

 labium can not be bent as it can in the forms which suck blood. 



In the males of many species the sheath of the proboscis shows a suture out- 

 wardly from the middle. Usually it is indistinct, but in the male of Deinocerites 

 there are chitinous margins connected by a membranous strip as in a true joint. 

 Its significance is not clear; perhaps it indicates the limits of the true labial 

 structures. It may be mentioned in this connection that Meinert considered 

 the sheath of the proboscis as of composite origin and formed mainly by the 

 greatly produced portion of that part of the head which he considers the ventral 

 plate of the first metamere. 



It has already been shown that there is a salivary duct in connection with the 

 hypopharynx. Macloskie found that there were two sets of salivary and poison 

 glands in connection with this duct. The glands are situated in the anterior 

 ventral part of the thorax and each set consists of three glands, two of which 



