I SCIENCE. '^5 



April 29, 1892.] j-yoL. XIX. No. 482 



THE SYSTEMATIC POSITION OF THE DIPTERA. 



Having been a student of the Diptera for two years, I have 

 come to the conclusion that the order is entitled to the dis- 

 tinction of being, as a whole, more highly specialized than 

 any other. Entomologists who have attempted a general 

 classification of insects have almost uniformly regarded the 

 Hymenoptera as the highest order, placing the Lepidoptera 

 second, and the Diptera third. The only exception in Amer- 

 ica. I believe, is Professor Hyatt, who, in a recent boolj: 

 ("Insecta," by Alpheus Hyatt and J, N. Arms), has placed 

 the Diptera at the head of the class, with the Hymenoptera 

 second, and the Lepidoptera third. His argument for this 

 arrangement is brief and forcible. The main features may 

 be summarized as follows: — 



The essential question which settles the rank of any insect 

 is. How far does it deviate in structure, and through what 

 line of descent has it developed, from its Thysanuriform an- 

 cestors ? To introduce the subject of instinct or of useful- 

 ness to man is to confuse our ideas, for we cannot translate 

 the data furnished by such a criterion into terms of the other 

 standard. Applying this principle, he takes the following 

 features of Diptera to show that they possess a degree of 

 specialization surpassing any other order: — 



1. Larval structure: " The young of even the generalized 

 forms of Diptera are, as a whole, farther removed from the 

 Thysanuriform type than those of any other group. Tiie 

 secondary larval form, which in the case of the Diptera is 

 always footless and often an almost headless maggot, has 

 complete possession of the younger stages. As Fi'iedrich 

 Brauer has pointed out, the general absence in the larvae of 

 Diptera of the thoracic legs, even although living in situa- 

 tions that seem to demand their development, shows that 

 they must have inherited this peculiarity from an ancestral 

 form whose larva had lost them. This compai'ative inflexi- 

 bility of the larval stage is suflRcient of itself to show that 

 there is now a wide gap between the existing Diptera and all 

 other orders of insects, and that this chasm is not closed by 

 the resemblances of the parts in the adult to those of the 

 Lepidoptera or isolated forms in other orders" (pp. 273, 274). 



2. The presence of but two wings: "The tendency to the 

 enlargement of one pair of wings, like the tendency to the 

 enlargement of certain pairs of thoracic legs and the reduc- 

 tion of other pairs, or a change in their structure and func- 

 tion, so that the insect makes a departure from the conven- 

 tional normal type of four equal membranous wings and six 

 equal-jointed legs, is everywhere an index of specialization" 

 (p. 274). 



