TIIK STICK-IXSKCT. 1 77 



shapes developed from tlie anterior end, eight long cyliudrienl 

 caeca in BlattidiB and Mantida?, two large i-nunded e?ect\ in 

 Locustida? and (Trylli'lff', or again six pouches in Aeridiid;e, which 

 may he further provided witli inferior appendages. In B. ?-ossii 

 these ca'ca (fig. 1, fig. 3, fig. T), C.) exist merely as small lobes 

 clustered together in small nund?ers and very i-udimentary. 

 These c;ieca must not be confused with the gland-like structures 

 (fig. 1, Ta.) which occur just anterior to the Mali)ighisin tubes. 

 Indeed it is not definitely known whether the function of these 

 latter so-called " glands " is really glandular, secreting a, digestive 

 • juice which is poured into the intestine, or excretory, eliminating 

 waste })roducts like the Malpighian tubes. At their point of 

 attachment to the gut these organs are pear-shaped, tapering 

 abruptly into a small tubular thread, the calibre of which is 

 about half the size of that of the Malpighian tubes amongst 

 which they pass. Heymons (1897) has shown that in origin and 

 morphology these tubular appendages bear a very close I'esem- 

 blance to the Malpighian tubes ; but physiologically he legards 

 the two sets of organs as difterent, since they are dissimilar 

 in their behaviour towards injections of coloured particles. 

 (Jenerally speaking, it was found that the tubular appendages 

 were the less sensitive, but they may eliminate some substances 

 quite as actively as the Malpighian tubes, a,s, for instance, Ehrlich 

 blue. If their function be excretory, it is less genei'al than that 

 of the ordinary organs of excretion. 



The intei-nal wall of the mid-gut is composed of a layer of 

 large cylindrical epithelial cells (PI. XXIX. fig. 5, E ; fig. 6, E 

 and E|) provided with a " striated border '"' (fig. 5 and fig. 6, Cb.), 

 and further they are characterised liy a continual secretion of 

 globules of mucilage (fig. 5 and fig, 6, Mg.), which are deposited 

 in the intestinal cavity. Cuenot (1895), amongst other authors, 

 describes the presence of J'oung cells in this epithelium undergoing 

 mitotic division and gi'adually replacing the older cells. These aie 

 of the nature of small interstitial cells with rather dense, deep- 

 staining nuclei ; but I myself have not observed any mitotic 

 figures in them. There is still dispute on the quevstion of these 

 so-called " germinative-centres," and many authoi-s, notai)ly 

 Frenzel (1886) and Visart (1894), consider them as glandular 



There is no pi'otective chitinous cuticle lining the internal 

 walls of the mid-gut, but its place seems to be taken by a very 

 slender peritrophic membrane (figs. 5 and 6, Mp,) which is quite 

 detached from the epithelium. It takes its origin at the point 

 where the fore-gut epithelium joins that of the mid-gut, and 

 extends as far as the hind-gut, whicli it enters for a short 

 distance. Thus the food passes through the alimentary canal 

 without the delicate epithelial cells running any risk of abrasion, 

 fi'om jagged particles eaten by the insect in the course of its diet. 

 This membrane (Trichter) is certainly not a prolongation of the 

 clutinous cuticle of the crop, as Mncznikow and Schneider (1890) 



Proo. Zool. 8oc.— 1912, Xo. XII. 12 



