OF MAXILLULSE IN THE ORDERS OF INSECTS. 439 



the dorsal wall, so that there was no doubt at all as to the exact position of 

 these plates. Chitinous sclerites (s.p.l) and (s.p.2) connect the outer edge 

 of each with the upper surface. of the hypopharynx. Distally arise sclerites 

 (s.m.) reaching to the apices of the delicate lateral lobes (m.). These lobes 

 bear the same relation to the hypopharynx as do the maxillre of Forficula, 

 and it seems highly probable, as Bonier (4) suggested, that they represent 

 these appendages in a somewhat modified condition. A pair of membranous 

 lateral projections (/.) arises behind them and may possibly represent a basal 

 lobe of the maxillulse. 



Attached to the base of each plate (p.) are the forks of a strong tendon (t.), 

 whose presence strongly suggests that the chitinous structures associated 

 with the hypopharynx are mechanical in function. 



In order to settle the question whether or not gland tissue is to be found 

 associated with the plates (p.), nymphal specimens of a small British species 

 of the Psocina group were sectionized. The fixatives employed were Oarnoy's 

 fluid (cold) and Gilson's fluid (hot), and the sections were stained with 

 Heidenhain's iron hematoxylin in some cases and Grenadier's hematoxylin 

 and eosin. The tissue lying between the plates and the upper surface of the 

 tongue was indistinguishable in structure from that seen in many parts of 

 the other mouth appendages. In transverse sections through the tono-ue no 

 histological difference could be detected between the median portion and that 

 lying above the plates. This investigation, therefore, lends support to the 

 assertion that these latter structures are not in any way glandular or asso- 

 ciated with glands. They are to be looked upon as thickened parts of the 

 ventral wall of the tongue, which may possibly have originated as linoual 

 stalks, or as the basal portions of maxillulse which have become incorporated 

 into the hypopharyngeal wall. 



NEUROPTEKA. 



RapJddia, — Adult forms of a species of MapMdia were examined and in 

 them the hypopharynx revealed some features of great interest. Text-nV 7 

 (p. 440) represents the labium and floor of the mouth as seen when viewed 

 from the dorsal surface; (p.) is the labial palp and (/.) the bifid, clorsally flexed, 

 extremity of the single median endite borne by the mentum. See West wood 

 (46. pp. 45-56). The opening of the salivary duct occurs above the labium 

 and ventral to the median fleshy projection (/<.) in the floor of the mouth. 

 This rounded lobe I regard as the hypopharynx or its distal portion. It is 

 almost obscured by two oihers of similar membranous texture (in.). Each 

 lateral lobe measures - 14 mm. in length and 'II mm. in width. In texture 

 and .relative positions these three lobes bear a decided resemblance to 

 the median hypopharynx and lateral maxilluhe of Forficula. Since the 

 Neuroptera are amongst the less specialised Endopterygota it is possible 

 that a true homology underlies this similarity. 



