178 ME. A. E. CAMERON 0X 



believed, but seems to be secreted by the most anterior epithelial 

 cells of the mid-gut. The question may be asked : How does 

 B. rossii assimilate its food ? This can only be explained by a 

 knowledge of the laws of osmosis, so that the digestive juices 

 secreted by the epithelium and the fluid juices which resiilt from 

 their action must pass through the membrane, the former to act 

 on the food .substances, the latter to be absorbed. 



Schneider (1890) and Adlerz have observed the presence of a 

 peritrophic membrane in diverse Orthoptera, Phyllodromia, Peri- 

 ■planeta, Bacillus, LoQusta, Forficida. This has been verified by 

 Cuenot (1895), who adds some details as regards its origin of 

 which little is known. 



Plateau (1875), in his splendid work ' Recherches sur les 

 phenomenes de la digestion chez les insectes,' has shown that 

 digestion first begins in the crop, where the alkaline or neutral 

 secretion of the salivary glands acts on starchy substances, 

 changing them to glucose. The processes of digestion are con- 

 tinued in the mid-gut, the epithelium of which also secretes a 

 fluid with alkaline or slightly acid properties which has the power 

 of changing albuminoids into peptones and of emulsifying fats. 



Petrunkewitsch (1899) held that in certain Orthoptera the 

 crop was the principal organ for the absorption of digested food, 

 citing as his proof the presence of fat in the epithelial cells. But 

 Sinety (1901) demonstrated clearly that the fat globules here 

 present are really elaborated by the epithelial cells from materials 

 extracted from the blood, and thus the epithelium of the crop is 

 functionally comparable to the fat-body. Again, many authors 

 adopted the idea that owing to the shortness of the mid-gut 

 supplementary absorption must be carried out in the crop 

 (Plateau [1876] and Jousset de Bellesme in the Blattidse), or 

 even in the hind-gut (Plateau [1878] and Frenzel [1886]). But 

 from all known laws of osmosis it is highly improbable that this 

 can be the case, for the thick chitinous cuticle lining both crop 

 and hind-gut is impermeable to dissolved substances. Again, it 

 is nothing short of absurd to suggest that absorption can go on 

 below the point of insertion of the Malpighian tubes which mark 

 the posterior limit of the mid-gut, and invariably pour their 

 waste-products into the alimentary caiial at this place. 



In B. rossii the Malpighian tubes (PI. XXVIII. fig. 1 and 

 PI. XXX. fig. 7, Mt.) are very numerous and are disposed re- 

 gularly in a circle round the anterior end of the hind-gut, into 

 which they open in groups of three to six. These groups, occurring 

 to the number of 20 to 30, are equidistant from each other, and 

 the tubes composing any one group fuse at the apex of a small 

 conical tubercle which arises as an evagination from the gut 

 and is traversed by a minute duct (fig. 7, Cd, and Cd^). The con- 

 stituent cells of the Malpighian tubes also possess the " ciliated 

 border " characteristic of the epithelial cells of the mid-gut, but 

 the " cilia " in both cases do not possess any power of motion 

 even in an indifferent medium. It cannot be argued that the 

 fact of the insect being dissected would cause the " cilia " to 

 cease vibrating immediately, as the cilia on the gill-plates of 



