796 MR. J. G. IT. FREW ON THE LARVAL 



though it couhl not be traced to any opening. Tlie gland cells 

 are probably modilied hypodoi-m colls. Keilin has described the 

 peristigmatic glands in several Oyclorrhaphous larva3. 



The anterior stigniatic trunks are surrounded as they traverse 

 the hypoderni by modilied hypoderm cells which are probably of 

 the nature of poristiginatic glands, although they are not nearly 

 such prominent structures as the posterior peristigmatic glands 

 and are apparently unprovided with ducts, 



IVie Albnentary Canal and its appendages. 



The structure of the pharynx has been described in connection 

 with the pharyngeal sclerites. The hypoderm surrounding the 

 ventral posterior arm of the pharyngeal sclerite is dii'octly con- 

 tinuous posteriorly with the epithelium of the oesophagus, which 

 is a straight, narrow tube with a very small lumen. In the first 

 abdominal segment it traverses the ganglionic mass, slightly jios- 

 terior to which it enters the cardiac valve (proven tricid us). This 

 is of the type commonly found in Dipterous larvie. It is a peai- 

 shaped body, its broad anterior end being continuous with the 

 cesophagus, its narrow posterior end Avith the cardiac division of 

 the midgut. Tne structiu'e of the proventricnlus is essentially 

 similar to the house-fly larva (see Hewitt, p. 1^7) and will not 

 therefore be described. Tiie cardiac ring of iniaginal cells occupies 

 the same position as it does in the larva of the house-fly and other 

 Dipterous larva;. 



The proventrlculus lies in the anterior region of segment 5 

 {2nd abdominal). From here the midgut runs backwards to the 

 anterior region of segment 10 ; turns dorsally and runs forwards 

 to the posterior region of segment 4 ; backwards to segment 6, 

 where its diameter decreases considerably ; forwards to the pos- 

 terior region of segment 5 ; backwards, its diameter increasing 

 somewhat, to the middle of segment 10 ; forwards as a wide, thin- 

 walled tube with a very poorly developed epithelium to the 

 posterior region of .segment 7, where it passes into the hindgut. 

 This last section of the gut is liable to become enormously 

 ■distended, when its epithelium becomes extraordinarily thin and 

 ill defined ; its contents are usually of a dark brown colour. 



No attempt has yet been made to work out the detailed 

 ■ histology of the different regions of the midgut. As mentioned 

 above, its last section was, in all examples studied, considerably 

 distended ; other regions of the midgut are also liable to dis- 

 tension, particularly the regions of the bends, and the appearance 

 of sections of the gut-wall varies veiy greatly according to the 

 degree of distension, great distension being frequently acconi[)a.nied 

 by partial degeneration of the epithelium of the aii'ected region. 

 The possession of a striated border is a constant characteristic of 

 the cells of all regions of the midgut epithelium, and this border 

 can usually be made out by careful examination even where the 

 ;gut is very greatly distended. There is no peritrophic membrane 



