102O.J 107 



maxillary palpi claimed h}' Wesclie to he present in ('yclorrliapha, and 

 more especially among the Acalypterae, are probably correctly regarded 

 by Peterson as being nothing more than the galeae of the maxillae. It 

 is likeh^ that the extremely forward position of the palpi in certain 

 Nematocerous families, correlated with the shortness of the labium, has 

 led Wesche to regard the palpi as pertaining to the labial and not the 

 maxillary somite. It will, furthermore, be recollected that Kellogg, 

 from a study of the larval head in Nematocera, observes that the 

 imaginal mouth-parts are found in unmistakable correspondence or 

 homologous relations with the larval counterparts. A similar result 

 was arrived at by Miall in his study of the head of Chiroiionu/s. 



In both Sinuilium and the Tahanidae the maxillae carry a minute 

 inner appendage which is very possibly a vestigial lacinia. If this inter- 

 pi'etation be correct, the principal lobe of the maxilla is the galea and 

 not the lacinia as believed by "Wesche. The largest number of complete 

 elements of the mouth-parts are found in the females of certain blood- 

 sucking and predaceous families {Culicidae, Simulidne, Dixidae, Sle- 

 pharoceridae, Tahanidae) which alone retain mandibles. Among males 

 the latter organs are extremelv rare, but Peterson finds that they are 

 present in species of SimuUum, and Wesche has recoi'ded their occur- 

 rence as an abnormality in some Culicidae. 



The absence of labial palpi makes it difficult to homologise and 

 correctly locate the sclerites of the labium — a difficulty which is 

 heightened by the extensive development of membranous areas. 

 Peterson's work leads to the conclusion that it is practically impos- 

 sible to differentiate between mentum and submentum, and the theca 

 which is usually homologised with the former sclerite would have to be 

 regarded as a separate and later chitinization. The epipharynx and 

 hypopharynx exhibit great constancj' of characters, which is particularly 

 striking when considered in connection with the modifications that have 

 resulted in all other parts. 



Turning now to the head itself. Peterson finds that the epicranial 

 sutures are present in the least modified condition in ATycetophila ; else- 

 where the median suture is either much reduced or wanting. The 

 V-shaped arms, however, are of wide occurrence, including many of 

 the cyclorrhaphous families. The fronto-cl^q^eal region, or area enclosed 

 by the arms of the V, is, according to him, always fused into a single 

 sclerite, devoid of demarcation between its component elements. In this 

 conclusion Peterson differs from other morphologists, and denies the 

 existence of a clypeus as a separate element throughout the order. 

 "What has been previously regarded as the clypeus is termed by him the 



