PROVENTRICULUS 37 



begins, and, enclosing the plug at the sides and above, it merges 

 into the wall of the ventriculus. T do not agree with Lowne, 

 who regards the proventriculus as "a gizzard and iidthin^ more," 

 but its structure suggests a pumping function and also that of 

 a valve. This interpretation of a combined pump and valve 

 operated at will by the fly is supported by the fly's method of 

 feeding and regurgitating its food, which habits will be described 

 later (p. 80). 



On the dorsal side of the oesophagus, at its junction with 

 the proventriculus, a small ganglion, the proventriculai- ganglion 



Pv. . 



9-^- Ven. 



OQS. 













■^ -■*'- ^ . dec 



Fig. 13. Section through the proventriculus and the anterior end of the ventri- 

 culus, to show the structure of the proventricular plug (Pep.) and the ducts of 

 the oesophagus (oes.) and crop ((Lcr.). (Camera lucida drawing.) 



(Pv.g.) lies, communicating by means of a fine nerve with the 

 cephalic ganglion; this forms a part of the sympathetic or visceral 

 nervous system. 



The Ventriculus, or Chyle Stomach (Veil.), represents the an- 

 terior region of the mesenteron, the posterior region of the latter 

 being formed by the proximal intestine. It is narrow in front, 

 and widest in the posterior region of the thorax, where it again 

 narrows in passing through the thoraco-abdominal foramen into 

 the abdomen to become the proximal intestine. Except in the 

 anterior and posterior regions, where columnar cells compose the 

 digestive epithelium, the walls of the ventriculus are thrown into 

 a number of transverse folds, which are again subdivided longi- 

 tudinally, the result being the formation of small crypts or sacculi, 

 which are lined by large cells. These sacculi correspond to the 

 digestive coeca of other insects. 



