304 ROBERT E. SNODGRASS. 



Near the middle are inserted several protractor muscles fig. 7, p. 

 to.), which are attached to the maxilla. On the posterior end are 

 inserted the retractor muscles (r. to.) whose origin is on the wall of 

 the head. 



The oesophageal sclerite and lingual glands (fig. 3) occur in typi- 

 cal form in nearly all the Ischnocera, but are absent in most of the 

 Amblycera. In the latter group they are present in probably all 

 the species of Colpocephalum, in most species of Menopon and in 

 Ltemobot/i rln in gypsis, but in these forms the sclerite does not have 

 the shape characteristic of it in the Ischnocera. In two previous 

 papers (8 and 10) the writer has given detailed descriptions of these 

 organs in several species. 



In the Ischnocera the oesophageal sclerite is nearly always of a 

 shield shaped form when viewed from above or below, is very convex 

 ventrally, has two wide anterolateral arms and a small median pos- 

 terior lobe, and has a chitinous band extending from each lateral 

 dorsal rim upwards toward the roof of the head. From its ante- 

 rior end a rather long duct runs forward which divides and goes 

 posteriorly to the lingual glands, which latter do not differ from 

 those of the Corrodentia. 



The sclerite is a thickening of the intima of the oesophagus and 

 is not a hypopharynx in the sense in which this term is used in 

 insect anatomy. The true pharynx of insects is of course the ante- 

 rior end of the (esophagus, but the word " hypopharynx " refers to 

 the median lobe developed above the base of the labium in the 

 cavity between the mouth parts, which is outside of the true mouth 

 located in the peristomal membrane. 



In those species of the Amblycera that possess an oesophageal 

 sclerite, the anterior arms of the latter are usually greatly elongate 

 and frequently there are postero-lateral lobes present. The body of 

 the sclerite is also relatively smaller and usually of an oval outline, 

 rather than shield shaped. Such a sclerite is shown in figure 3 (ce. . 

 scl.), representing in ventral view that of Lwmobothrium gypsis. In 

 this species the anterior arms are long thin plates slightly expand- 

 ing at the anterior ends. The lingual glands are proportionately 

 small and are ovate in shape. (The left gland is removed to show the 

 anterior end of the left arm of the sclerite). 



The histology of the oesophageal sclerite and the lingual glands 

 has never been investigated, and their function is yet to be explained. 



