PeritropJiic Meiiibrane of Stomach 59 



also is lined by a cliitiiious tube, wliicli is not usually in 

 contact with the epithelium. This is the funnel (Trichter) 

 of Schneider, the peritrophlc memhi'ane of Balbiani. Its 

 chitinous nature is inferred from its resistance to alkalis. 

 It invests the food, and may be a provision for keeping- 

 rough particles from abrading the delicate epithelium. 

 At times of moult, and in some Myriopods and Crustacea 

 at all times, the peritrophic membrane breaks off, and 

 passes out of the stomach with the faeces, which are thus 

 enclosed in a kind of bag. In the Chironomus-larva it 

 can at times be seen to begin exactly where the mesen- 

 teron begins ; sometimes its fore edge is included in the 

 first fold of the epithelium of the mesenteron (fig. 48). The 

 peritrophic membrane has been found in nearly every 

 ]3ipterous larva examined ; Dicranota is an exception. 

 It occurs also in many insects of other orders. 



AVe have not been able to obtain entirely satisfactory 

 evidence of the actual formation of the peritrophic 

 membrane in Chironomus. In the larva of Simulium 

 there may occasionally be seen a very copious fluid, 

 coagulable by alcohol, in the cardiac caeca, and investing 

 the food in the stomach. We have thought it possible 

 that this may be the peritrophic membrane in a nascent 

 condition. The membrane may in Chironomus also be 

 a special secretion of the cardiac caeca, but of this we 

 have still less evidence. Gehuchten (Ptychoptera), 

 Cuenot (Orthoptera), besides Plateau and Balbiani 

 (Chilopoda), agree that the membrane originates in tlie 

 mesenteron. 



The membrane extends throughout the stomach, though 

 without attachment to its wall, except at its fore end, 



Schneider, 1887, p. 95), in some Myriopods, Crustacea iCirrii^eds, Clado- 

 cera), and Gasteropoda (Limnaeus, Helix, Limax). Refei'ences to the 

 literature are given by Balbiani, 1890, p. 30 ; Schneider, loc. cit. ; and 

 Gehuchten, 1890, p. 91. 



