1913] Kershaw — The Alimentary Canal of Flata and other Homoptera 177 



parts in contact with the delicate walls of the organs directly into 

 the rectum or posterior part of the gut; thus avoiding passage 

 through the long and tortuous midgut, but leaving the more 

 nourishing matters to take the ordinary course through the whole 

 canal. This would, in fact, be supplementing the action of the 

 peritrophic membrane, whose chief function seems to be that of 

 separating the useless from the useful portions of the food — or 

 rather, retaining the indigestible matter within the membrane 

 till its evacuation from the anus. Certainly the twisted loops of 

 the gut are in intimate contact and their tissues even in part grown 

 together or fused : from which cause this part of the gut is difficult 

 to disentangle without injury. Feeding the insects on colored 

 liquids tends to confirm this theory, since the contents of the long 

 loop of the midgut are very faintly if at all tinted, whilst the rec- 

 tum is heavily colored. 



The epithelium of the reservoir (fig. 4) is formed chiefly by low 

 but very irregular cells, which appear to be in a constant state of 

 degeneration and renewal. In sections from a long series of 

 reservoirs of Siphanta during almost every month of the year, 

 there was not one with a moderately perfect epithelium ; but one 

 reservoir of Perkinsiella was once obtained in very good (appar- 

 ently resting) condition, out of a long series. The young cells 

 have a single nucleus, but the older ones are mostly bi-nucleated, 

 though very often a cell will have but one enormous nucleus. 

 The epithelium of the caeca is similar but usually in rather more 

 perfect condition, and seems to be constantly renewed by young 

 cells at the bottom or end of the caeca. The cells of the reservoir 

 are in one place or another apparently always secreting; after a 

 time the nuclei become much larger and irregular in shape and 

 the cells become detached from the basement-membrane, or are 

 thrust from it by the new cells. When several contiguous cells 

 become detached they seem to carry with them part of the inter- 

 cellular cement or membrane, which shows in sections as an irreg- 

 ular reticulum; or it may be the cell-walls persisting longer than 

 the contents. The cast-off cells generally assume a more or less 

 globular form (probably on escaping from the lateral pressure of 

 adjoining cells of the epithelium) and rapidly disintegrate, the nuclei 

 becoming less and less distinct; finally the cells appear to become a 

 granular and somewhat viscid fluid (probably the granules rep- 



