176 MB. A. E. CAMERON ON 



The fore-gut up to and including the crop is of rather simple 

 structure. As a rule the histological structure of the insect 

 alimentary canal is always the same : on a layer composed of 

 muscular and connective tisssue there rests an epithelium which 

 secretes a strong chitinous lining. This cuticle is raised into 

 straight longitudinal ridges which bear numerous minute horny 

 denticulations. The pharynx of B. rossii (fig. 1, Ph.) is very 

 short and is lodged in the posterior cephalic region, the oesophagus 

 (fig. 1, Q5.) occupying the elongated prothorax and passing 

 insensibly into the somewhat dilated crop (fig. 1, Cr.) in the 

 region of the mesothoi'ax. Lastly, the crop joins the mid-gut 

 (fig. 1, Gm^) in the region of the metathorax, and, indeed, the 

 internal wall of the crop is telescoped into the cavity of the 

 mid-gut as a cone-shaped prolongation (Riissel). But in addition 

 to what may be called the primary direct extension of the crop 

 (PI. XXIX. fig. 5, Ovj and Ovja) there is also a secondary 

 indirect extension (fig. 5, Ov^ and Ov2a)- The chitinogenous 

 epithelial cells of the wall of the crop extend backward into 

 the mid-gut for a short distance as far as the point A denoted 

 in the figure. They then become folded back on themselves up 

 to the point B, and turning once more form the long dorsal pro- 

 longation which reaches a comparatively long way into the mid-gut. 

 At C the cells are again reflected, and finally at D join with the 

 larger epithelial cells of the mid-gut. The chitinous cuticle lining 

 the prolongations is continuous with that of the ci'op. From fig. 5 

 it will be observed that the extensions are not symmetrical but 

 are much more pronounced dorsally than ventrally. This un- 

 symmetrical arrangement is known to occur only in the few 

 Phasmids in which the alimentary C0,nal has been investigated, 

 and the exact reason of the greater development of the dorsal 

 lamina is not known. In the larvse of Chironomus the oesophageal 

 telescoping is uniform and symmetrical, and I believe that this is 

 the case with the majority of insects where the telescoping occurs. 



Heymons (1897) gives it as his opinion that the elongate 

 dorsal lamina (Verschlussklappe) functions as a closing-valve, 

 preventing the back-flow of digested food from the mid- to the 

 fore-gut. But Binety (1901) does not agree with this interpre- 

 tation, as he is convinced that if the direction of the food-curi-ent 

 were to be reversed this flap woiild be overcome by the pressure. 

 The bundles of circular muscle svirrounding the anterior part of 

 the mid-gut would be quite effective in checking the reversed 

 food-current if any such occurred. 



The mid-gut of B. rossii is divided into two distinct parts, of 

 which the anterior is characterised by very prominent transverse 

 folds (PL XXVIII. fig.. 1, Gm^ ; fig. 3, Gm, ; PI. XXIX. fig. 5); 

 while the posterior (fig. 1, Gm^), besides being narrower, is easily 

 distinguished by the presence on its external walls of numerous 

 (about 50) conical, tubular organs (fig, 1, Ta,), 



In all Orthoptera as before stated, except the Phasmidse, the 

 surf^3 of the mid-intestine is enlarged by diverticula of various 



