LARVAL HEAD OF SOME CHIRONOMIDAE — GOUIN 



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arched, its internal wall is very thick, both walls dorsally and laterally 

 are quite far apart, thus leaving a wide space. So on preparations in 

 toto the hypochilum appears to have small winglike expansions to the 

 right and left of the median part. This conformation of the base of 

 the hypochilum has been recognized by several authors (Pagast, 

 Strenzke, Zavfel, and others) who designate it by different terms such 

 as "Orimente," "Fliigelpartieen," "lamina basalis." 



Fig. I. — Psectrocladius cf. psilopterus K. 



Typical orthocladian structure. Ventral view of the anterior part of the head. 

 The labral chaetae {ch) number about a dozen; the lateral hypochilan teeth 

 are supported by the interior wall as in all the other forms. The situation of the 

 salivary duct and pump {CS) is indicated by stippling. Cf. figs, i, 2, and 3 of 

 Gouin (1957), and figs. 3, 5, 6, and 7 of this paper. 



These "laminae" are only the lateral parts of the hypochilum and 

 are, moreover, much enlarged. They are therefore not homologous 

 with the chironomian paralabial plates ; on this point also the ortho- 

 cladian structure appears as a simplified chironomian structure. 



These buccal organs serve to scrape the surfaces of flints, rocks, 

 branches, etc., whereas the chironomian structure is rather of use in 

 dealing with a soft substratum such as slime or fine particles collected 

 in the tube. This "lasiophagous" structure (Gouin) is present in the 

 numerous species of the subfamily Orthocladiinae (s.l.), species 

 populating the most diverse aquatic habitats as well as some that are 

 terrestrial. One must expect to find numerous variations of this struc- 



