44 MOSQUITOES OF NORTH AMERICA 



which, in the female, is formed by the labium alone. Whether the joint near the 

 middle of the labium of the male Culex is true or false I cannot say, since I 

 have never seen it bent by the insect itself; its appearance is that of a true joint. 

 Like the labium of the female, that of the male has two longitudinal main 

 tracheal stems (figs. 12-14, tr), and two rows of longitudinal muscles." 



Kraepelin expressed the opinion that the labrum is not formed by the union 

 of two pieces, the labrum and epipharynx, but that it is an evagination of the 

 head and in consequence necessarily hollow. " It can therefore, as all body- 

 appendages are evaginations and consequently hollow, impossibly be interpreted 

 as the fusion of an upper and lower lamina." 



Becher was of the same opinion and states that the so-called epipharynx of 

 the Diptera is never found as a free part ; he calls the part the lower lamella of 

 the labrum. 



Meinert has traced the course of the salivary duct and found that it differs in 

 the two sexes. His interpretation of the hypopharynx does not agree with that of 

 Dimmock. In the female Meinert found that the salivary duct penetrates the 

 posterior part of the hypopharynx; before entering it forms a large receptacle 

 from the upper part of which a strong muscle extends to the under side of the 

 pharynx. " In the male the hypopharynx does not protrude but is very short 

 and rounded anteriorly and the salivary duct runs through the entire sheath 

 [labium] along the under side of its floor until it terminates in the tongue." 



Wesche considers the hypopharynx of the male as long, like that of the fe- 

 male, and the " tongue " of Meinert, protruding between the labellge, as its apex. 

 He speaks of the ciliation of the free apex, which he states to be present in all 

 males, as " a surprising reversion " ; perhaps it can be explained as readily as an 

 adaptation to the feeding habits of the male. One gets the impression from 

 Wesche's paper that he believed that the hypopharynx is free in the male 

 throughout its entire length ; such does not, however, appear to be the case. He 

 figures the abnormal mouthparts of a male Anopheles maculipennis which ap- 

 proach those of the female. Not only the mandibles and maxillae are present, but 

 also a free hypopharynx which extends to the tip of the proboscis. 



The mandibles of Diptera are present only in the females of the blood-sucking 

 orthorrhaphous forms. Becher, whose work has been criticized for its inexact- 

 ness, states that two parts can usually be clearly distinguished in these organs : 

 " a basal piece, which lies in the interior of the head, and the mandible proper, 

 which can be moved upon this base by means of a joint." None of the students 

 who have followed exhaustive methods appear to have detected any such joint. 

 Becher's interpretation of the mouthparts is at variance with the commonly 

 accepted homologies in various details but his paper is neither clear nor con- 

 vincing. Furthermore, he commits the error of basing his views on studies of 

 the mouthparts of the higher Diptera and interpreting the lower forms from this 

 standpoint ; thus we can, with the more propriety, pass over a detailed considera- 

 tion of his work. It may, however, be pointed out in passing, that while Becher 

 rightly, we believe, rejects the idea, held by some of the earlier authors, that the 

 maxillaB and even the mandibles may enter into the composition of the labium 



