450 



MISS A. M. EVANS ON THE STRUCTURE AND OCCURRENCE 



appearance shown in t .>xt-rjg. 16. Between the vestigial labial palpi (in.p.) 

 projects the rectangular flat membranous structure (A.). Since this structure 

 lies above the labial duct it is here considered to be the hypopharynx. It 

 is supported laterally by two arms of the skeletal system. The length is 

 ■08 mm. and the greatest width '09 mm. The dorsal surface is markedly 

 convex and bears two large convex plates (m.) covered with rows of minute 

 spines. I regard these plates as maxillulse, which have become flattened in 

 accordance with the dorsi-ventral compression of the head. 



A comparison between the anterior aspect of the labium and hypopharynx 

 oi.Sialis and Selandria (text-figs. 8 & 15) reveals a close agreement with regard 

 to the arrangements of the constituent elements. The salivary opening in 

 both cases causes a slit-like depression above the border of the labium. 



Text-%. 1G. 



mx 







(i f! fp 



^n'fV V' V' ' ^ Ufa* 



Fenusa melanopoda. Hypopharynx and maxillulse, dorsal aspect. The maxilla is 

 indicated on the left side only. X 400. h. Hypopharynx. m.p. Labial 

 palp. m. Maxillula. mx. Maxilla. 



Dorsal to it is a median lobe, the hypopharynx, whose lateral lobe-like 

 expansions form the lateral walls of the depression. These latter are asso- 

 ciated with the labium at each side behind the base of the palps. In Sialis, 

 however, the ligula of the labium exists as a definite setose plate which its 

 not represented in Selandria. This comparison points to the conclusion that 

 the labium and hypopharynx of Neuroptera and larval Tenthredineae are 

 constructed on the same fundamental plan. 



In discussing the labial gland of Tenthredinian larvse, Berlese (1. p. 522) 

 described its termination " sotto la lingua in una specie di filiera." This 

 leads us to enquire how far the condition here may be compared with that of 

 Lepidoptera. 



We have noticed that the labium in larval Tenthredineae is in a con- 

 siderably reduced state, while in Lepidoptera it has become almost 



