36 jouenaij of entomology and zoology 



Occasionally there are slight variations as to the number of rows. 

 Slightly cephalad of the point where the fore-intestine meets the 

 mid-intestine, is an invagination of the epithelium with its thick- 

 ened intima into the lumen, forming two projecting valves which 

 are capable of completely closing it. (Figs. 2, 4, 7, 9, V.) A 

 projection from the wall of the proventriculus (Fig. 7, St.) fits in 

 between the valves and makes the stoppage more complete. The 

 furrow formed between the valves and the wall of the canal is lined 

 practically along its entire extent with forwardly-directed, closely- 

 set spines also arranged In parallel rows. The surface of the 

 valves bordering on the lumen Is destitute of spines. 



The oesophageal valve (Figs 4, 9, Oe. v.) extends into the mid- 

 intestine for about one-sixth of Its length, and is continuous with 

 the two valves which are In front of It. It is very peculiar in that 

 it is not a complete tube, but Is open along the entire side where 

 the free ends of the valves approach each other. (Figs. 8, o, 9.) 

 The edges of the oesophageal valve along this opening are thick- 

 ened and folded and bear many little chitlnous tooth-like projec- 

 tions on their surface. (Fig. 9, F.) There Is also a narrow 

 circular band of similar teeth (Fig. 9, Cb.) on its outer surface, a 

 short distance from its distal end. 



III. Histology of the Proventriculus 



When considered histologically, the proventriculus of Hydro- 

 psyche presents some Interesting features. These relate especially 

 to the method of formation of the chltin, the epithelial layer under- 

 lying the teeth, and the arrangements of the muscular layers. 



A cross or longitudinal section taken through this organ shows 

 the following layers, beginning at the lumen and passing outward, — 

 the intima, the epithelium, circular muscles and longitudinal fibres. 

 (Fig. 4, Ch., Ep., Cm., Lm.) Each of these will be discussed in 

 turn. 



A. The Intima. The intima is a non-cellular layer, which has 

 become heavily chitinized in parts. It is modified to form teeth 

 in the anterior and spines In the posterior region. There are thirty- 

 six teeth which are greatly strengthened by chltin at their apices. 

 When the teeth of Hydropsyche are compared with those figured 



