790 



MR. J. G, U. FREW ON THE LARVAL 



that of a trough wifcli a double ventral wall, the space between 

 the two ventral walls being the cavity of the pharynx. The 

 trough is surrounded by liypoderuiis and the cavity of the trough, 

 4>,bove the pharynx, is also lined by hypodermis, the two layers 

 being continuous round the posterior end of the trough. (This 

 hypodermis is only shown in text-fig. 5, I) & E.) The dorsal 

 edges of the trough are joined together by a sheet of hypodermis 

 (wliich is really double though its double nature is never very 

 distinctly visible in sections) which appears to secrete a thin 

 layer of cnitin in places. I consider that this double layer of 



Text-figure 5. 



'JVausver«o sections through the points marked A-E in text-fig. 3. 

 -Chitin shown bhick or dotted according to the density of the chitin. Hypoderm 

 and dorsal membrane cross-hatched. The complete hypoderm is shown only 

 in text-fig. 5 E. It is partially shown in 51); not at all in the other 

 figures. 



hypodermis is homologous with the hypodermal fold in the larva 

 of Chirononiits, which is derived from the dorsal region of junction 

 of head and neck and extends backwards into the thorax and 

 from which arise the cephalic imaginal discs (14). In Chlorops 

 the cephalic imaginal discs arise from the posterior end of this 

 double hypodermal sheet. In the region i-epresented by text- 

 fig. 5, A tfe B, the dorsal membrane is present, but I am very 

 doubtful as to its nature, as I failed to find any hypoderm in con- 

 nection with it. It may possibly be chitinous, which is certainly 



