BY R. J. TII.LYARD. 297 



the Panorpoid and Neuropterous (s.str.) Orders were originally 

 semi-aquatic. The habit is still retained by Nannochorisla, and 

 probably also by the Choristhia , in Mecoptera, by the Tipulid(f 

 and many other families in Diptera, by the Chaidiodince in 

 Megaloptera, and by the OsmylidcK in Planipennia. From such 

 an archaic form of life- history, the development of true aquatics 

 (e.g., Sialincr,, Trichoptera), of false aquatics (e.g., Cidicidce), and 

 of land-dwellers is easily traceable. 



Gcenogenetic Characters. 



1. Heductioii hi size. - Naiinochorista is by far the smallest of 

 all existing Mecoptera. The reduction closely parallels that of 

 many Dipterous families, e.g., the relationship of Nannochorista 

 to PaiLorpodes and allies is closely analogous to that between 

 Culicidce and 7'ipulid(e. 



2. Loss of macrotrichia from wing-membi-ane. — Almost all 

 Mecoptera show macrotrichia more or less abundantly upon the 

 wing-membrane. In Naiinochorista, the wing-membrane re- 

 sembles that of many Diptera and Hymenoptera, a state that 

 may also be due to the elimination of macrotrichia. 



3. Reduction of the suh-costal vein. — This is especially evident 

 in the hindwing. Compare the hindwing of Lepidoptera. 



4. Loss of first apical fork. — This is unique amongst Mecoptera, 

 but is the normal condition throughout the whole of the Diptera 

 Brachycera. 



5. Highly specialised conditioit of fusion between M and Cuj. — 

 The amount of fusion between these two veins, and the far 

 distal position of the departure of M from M-f Cuj, are quite 

 unique in Mecoptera. It seems to me that a similar condition 

 exists in the Hymenopterous wing, and that the homologies of 

 the veins in that Order could be determined by reference to an 

 original Panorpid-like ancestor, in which a similar fusion had 

 become a fixed character; and, on this fusion, all later develop- 

 ments must have been based. 



6. High specialisation of mouth-parts. — The great reduction of 

 the mandibles, the formation of the sharply-pointed labrum 



