Cardia 55 



often called proveiitr/culus, in the belief that it is, like 

 the crop or gizzard of many insects, a dilatation of the 

 oesophagus. Weismann indeed expressly asserts that it 

 is such ^ Our sections of Chironomus- embryos (fig. 127) 

 lead us to a different conclusion, Avhich is confirmed by 

 the study of other insects. In Ptychoptera ^ Dicranota ^, 

 and the cockroach '^ the break in the epithelium is quite 

 unmistakable, and shows that the outer wall, which 

 in the cockroach is drawn out into caecal projections, is 

 mesenteric and not stomodaeal. The bee ^' and many 

 other insects show essentially the same structure. The 

 chitinous lining of the stomodaeum can often be distinctly 

 traced as far as the break in the epithelium, where it 

 disappears ; in other cases the peritrophic membrane 

 described below introduces complications, or the chitinous 

 lining disappears graduall3^ "We believe that all or very 

 nearly all of the outer wall of the tube which encloses 

 the oesophageal valve is developed from the mesenteron, 

 and that caeca in this region always belong to the 

 mesenteron. It is therefore inappropriate in our 

 opinion to apply the term proventriculus to the part 

 in question, which when distinct we call the cardia, 

 or the cardiac chamber of the stomach. The term pro- 

 ventriculus has been long associated with the gizzard of 

 insects. 



The cardiac chamber, or beginning of the stomach, lies structure 



11 mi of stomach. 



in the metathorax ; it is externally well marked. Ihree 

 sets of short caeca project from its outer surface (fig. 41) ; 

 they have no muscular wall ^. A pair of muscles, arising, 



' 1863, p. 35 and fig. 96. - Geliuchten, 1890. 



•' Miall, 1893, fig. 18. 



* Miall and Denny, 1886, fig. 64, p. 120. 



* Schiemenz, 1883. 



* These caeca vary much in different Dipterous larvae; they are usually 

 short, but long in the blow-fly larva ; the number may be two (Cteno- 

 phora), four (Tipula, Simulium, &c.), or many. 



