448 MISS A. M. EVANS ON THE STRUCTURE AND OCCURRENCE 



The hypopharynx (text-fig. 14) measures "25 mm. in length and '22 mm. 

 in greatest width in an almost fully-grown larva. In its median portion the 

 upper surface is thrown into a pair of convex ill-defined lobes (m.) set with 

 stout curved spines. Each is supported externally by a chitinous plate (p.) 

 measuring - 05 mm. in length and '03 mm. in breadth. The free edge of 

 this plate is furnished with long hook-like spines. It arises from a chitinous 

 lateral expanse (a.m.). This latter is seen to be continuous ventrally with 

 the thickened portion of the mentum and is apparently homologous with 

 the chitinous "arms of the mentum " in Lepidoptera. (In the larva of a 

 Limopliilid a narrow bar of chitin is found in this situation.) The condition 

 of the mouth-floor in Hydropsyclie sp. was similar to that of Rhyacopliild sp. 



It has been shown that paired lobes associated externally with chitinous 

 plates occur in widely separated families of Trichoptera. This evidence seems 

 to suggest that the possession of these structures is a feature characteristic of 

 Trichopterous larvse with certain, exceptions. The hypopharynx, when these 

 structures are present, is comparable in constitution to that of the more 

 generalised Lepidoptera. In addition to the sctiferous lateral lobes, it is 

 characterised in both orders by (1) the possession of a conical spinneret, 

 (2) the presence of chitinous arms extending from the mentum and associated 

 dorsally with the exterior of the base of the lobes, and (3) the membranous 

 rounded nature of the floor of the mouth. Thus the hypopharynx of 

 Trichoptera is seen to be constructed on a plan fundamentally similar to 

 that of Lepidoptera. The maxillulse of the latter order are therefore 

 in all probability represented in Trichoptera by the similarly located 

 lobes (»!.). 



HYMENOPTERA TENTHREDINEJi;. 



A vertical section through the head of Hijlotoma rosce Berleso (1. p. 522, 

 fig. 595) shows that the duct of the labial or spinning gland runs above 

 the labium to open above its extremity. Dorsal to the duct is seen a fold 

 which constitutes the mouth-floor. The distal portion of this fold is, in all 

 probability, the hypopharynx in Tenthredinian larvse. 



In a recent paper on the immature stages of the Tenthredinoidea 

 McGillivray (Zl) fully describes and figures the mouth-parts of Pamphilius 

 dentatus. It is stated that in Pamphilius, " On the dorsal surface of the 

 ligula and laterad of the labial palpi, there is on each side a protuberance, 

 a paraglossa. Between the labial palpi and arising on the ental surface, 

 there is a prominent lobe which represents the glossa. The glossa has been 

 modified into a spinneret (figs. [), 13, sp.) for the opening of the duct of 

 the silk glands." In fig. 13 the spinneret is seen as a structure projecting 

 beyond the ventral surface of the ligula. It is therefore probably more 

 highly developed than in the forms to be described. 



