II FLIES WITH AQUATIC LARV^ 159 



bringing a supply of the minute organisms which 

 serve the larva for food. 



The description of Reaumur, given above in a 

 condensed form, is in the main a true and satisfactory 

 account. He was, however, mistaken in supposing 

 that the larva turns its back upwards, and that the 

 legs are borne upon the dorsal surface. Moreover 

 Reaumur was quite ignorant of the transformations 

 of Dixa. His successor, De Geer, in this as in many 

 other cases, added fresh information on points left 

 incomplete by Reaumur. De Geer^ reared the fly, 

 which he identified as a kind of Tipula. He gives 

 descriptions and figures of all the stages. De Geer 

 shared Reaumur's mistake as to the dorsal and 

 ventral surfaces. Meinert has given the best modern 

 account of Dixa, and has supplied excellent figures 

 of the details of structure of the larva and pupa.^ 



The structure of the larva can be gathered from 

 the figures here given (Fig. 47). The body is bent, 

 as Reaumur says, into the form of a siphon, the fifth 

 and sixth segments behind the head forming the 

 bend. The surface which comes uppermost is, as 

 usual, the dorsal surface, and the locomotive organs 

 are ventral. They consist of two pairs of pseudopods 

 or prolegs, armed with hooks, and borne upon the 

 fourth and fifth segments. On the eighth, ninth, and 

 tenth segments are bunches of setae which answer to 

 some extent the same purpose ; these are called legs 

 by Reaumur. At the tail-end and on the dorsal 

 surface is a respiratory cup, of the same nature as 



^ Hist, des Ittsectes., Tom. VI. p. 380. 

 ^ De eucephale Myggelarver (1886). 



