169 



specialized forms of the present day. In this paper a large series of 

 figures of heads of larvae belonging to all the principal sections is 

 given in order to exemplify the evolutionary phases and, incidentally, 

 to permit the student to judge as to the correctness of the classifica- 

 tion by a comparison of the available data thus presented in the most 

 readily comprehensible manner. An unillustrated discussion of ana- 

 tomical details affords no check on possible misstatement or misin- 

 terpretation by an author or on misconstruction of his words by the 

 student, and to prevent error from one source or another such dis- 

 cussions should be accompanied by figures. 



Brauer divided the Orthorrhapha into three tribes, Eucephala, 

 Polyneura, and Oligoneura, using the structure of the head as his 

 primary character in separating the groups, Eucephala having the 

 head entire, the others having the head-capsule incomplete posteriorly. 

 Oligoneura has in addition to an incomplete head-capsule vestigial 

 mandibles, a character which separates the tribe from the other two. 

 Brauer's classification has been generally accepted, though several 

 writers have pointed out what they consider to be errors in grouping 

 that result from the application of his rules, and Sharp has gone so 

 far as to suggest that his system has been influenced by his use of 

 dichotomic tables*. 



Recently a suggestion has been made that as the group Nema- 

 tocera is apparently an unnatural one, containing, as it does, some 

 widely dissimilar families which fall together according to Brauer's 

 classification, we should attach primary importance, not to the struc- 

 ture of the head but to the respiratory systemf . Here, again, an 

 arbitrary attempt has been made to divide the group Nematocera into 

 two tribes, Oligoneura and Polyneura, using the respiratory system 

 as a basis for the division. In some respects the suggestion is an im- 

 provement upon Brauer's system of classification, but even so, the 

 composition of both groups shows some confusion which to my mind 

 proves that the respiratory system is not an ideal character on which 

 to base tribes. In fact the only point clearly shown is that some 

 species of all of the families of Oligoneura, rarely, all species of some 

 of them, are peripneustic and hence assumably primitive structurally, 

 while all species, so far as is known, in Polyneura are amphipneustic, 

 metapneustic, or apneustic. That there are both metapneustic and 

 apneustic forms in Oligoneura of this latter classification, and that 

 several have the lateral abdominal spiracles functionless and may 



*Verrall's "British Flies", Vol. 5, p. 31. (1909) 

 tKnab, in Ann. Ent. Soe. Amer., Vol. 7, 1915, p. 93. 



