LARVAL HEAD OF SOME CHIRONOMIDAE — GOUIN 



193 



these swaying movements carry away the ingested prey and lacerate 

 its integuments. The return of the organ to its rest position is assured 

 by the premental muscle, acting on the premental basis. This same 

 muscle, quite strong in Macropelopia but very slender in Chironomus, 

 gives the labium a backward movement, the opposite movement being 

 effected by the elastic membranes alone or combined with the action of 

 the retractor angulorum oris. 



M/hdm 



Fig. II. — Macropelopia cf. ncbttlosa Mg. 



Part of a cross section passing through the pharyngeal ventral and lateral 

 dilators (M Ph vl), which are situated behind the circumoesophageal connective 

 and might correspond to No. 44 of Snodgrass (1929). The section meets the 

 salivary ducts immediately behind their point of union. 



THE LARVAL FORMAL TYPES IN CHIRONOMIDAE 



The organization of the predaceous Tanypinae larvae, the close 

 correlation of which with behavior we have just mentioned (p. 187), 

 differs from that of the orthocladian (s.l.) larvae by a set of charac- 

 teristics of which the "dominant" ones are : ( i ) the extreme de- 

 velopment of the cibarial and pharyngeal cavities and, correlatively, 

 of the radial and circular muscles just as in the case of the clypeo- 

 frons ; (2) the labroepipharyngeal armature is extremely reduced; 

 (3) the form of the mandibles and their movements in a horizontal 

 plane ; (4) the particular structure of the labiohypopharyngeal com- 

 plex which assumes the transport of the ingested food, while in the 



