6o 



Tlie Larva of Chironomus 



Miss Phil- 

 lips' ac- 

 count of 

 the oeso- 

 phageal 

 valve. 



and forms a loose inner tube of relatively small diameter 

 (fig. 39, ]pm) ; sometimes it is thrown into loops or bends 

 wHicli do not affect tlie stomach itself. Black masses of 

 food usually occupy the inner tube, and distinguish it 

 from the surrounding cavity of the stomach. At the 

 beginning of the small intestine the chitinous intima of 

 the proctodaeum begins, and a little beyond this place 

 the peritrophic membrane thins out and ceases. If the 

 alimentary canal is removed from a fresh larva, and 

 divided at the junction of the stomach and small intes- 

 tine, the muscular and epithelial coats above the section 

 contract, while the chitinous tube lies passive, and soon 

 protrudes considerably from the cut end. This gives 

 a ready proof of the want of adhesion between the mem- 

 brane and the surrounding epithelium ^. 



At our request. Miss Dorothy Phillips, a student of the 

 Yorkshire College, has investigated more fully the struc- 

 ture of the oesophageal valve and peritrophic membrane, 

 and furnishes us with the following account, as well as 

 with sketches for the accompanying illustrations : — 



' The oesophageal valve of the Chironomus-larva is 

 a complicated structure, and will be better understood 

 when compared with a simpler case. Simulium has been 

 chosen as a convenient term of comparison, 



' The layers of the oesophageal wall of the larva of 

 Simulium and Chironomus, in order from within, are as 

 follows ; — 



' Vignon (1899) has published a preliminary note on the histology of 

 the alimentary canal of the Chironomus-larva, in which he. •^tates(I) that the 

 cavities or transparent spaces beneath tlie striated hem of the cells of 

 the gastric epithelium are not visible in the living larva, and are due to 

 pressure or the action of reagents ; (2) that the peritropliic membrane is 

 secreted in the neighbourhood of the gastric caeca, and gradually pushed 

 downwards by the i^ressure of tlie food extruded from the oesophagus ; he 

 describes certain details, for which wo must await the fuller account to be 

 published in Arch, de Zool. exper. ; (3) that vibratile cilia occur in the 

 stomach and beginning of the intestine. 



