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 STEUOTUBE, DEVELOPMENT, AND BIONOMICS OF HOUSE-PLY. 527 



membrane which occurs in this region iu numerous insects, 

 and which has been studied in detail by Vignon (1901) and 

 others. Below the epithelial cells a number of small cells 

 (g. c.) are found, which may be either gland cells or young 

 epithelial cells. In addition to these cells small groups of 

 deeply-staining fusiform cells (i. c.) are found below the 

 epithelium. These, I believe, are embryonic cells from 

 which the mesenteron of the imago arises. The Malpighian 

 tubes arise in the tenth segment at the junction of the ven- 

 triculus and the intestine. 



The intestine (fig. 29, int.] is narrower than the ventriculus 

 and runs forwards as far as the eighth segment, where it bends 

 below the visceral mass and runs posteriorly, to become dorsal 

 again behind the tenth segment, from whence it runs back- 

 wards, turning ventrally behind the visceral mass to become 

 the rectum. The epithelium is thrown into a number of folds 

 and is covered with a chitinous intima. 



The rectum (r.) is very short and muscular, and the chitinous 

 intima is fairly thick and continuous with the outer cuticular 

 layer of the chitinous integument. It is almost vertical and 

 opens by the anus on the ventral side of the terminal larval 

 segment between the two swollen anal lobes. 



Salivary glands. There is a pair of large tubular 

 salivary glands (s. gl.) lying laterally in segments five and six. 

 Anteriorly each is continued as a tubular duct; the two ducts 

 approach each other and join beneath the pharyngeal mass to 

 form a single median duct (fig. 19, sal. d.} which runs forward 

 and opens into the pharynx on the ventral side as already 

 described. The glands are composed of large cells (fig. 21), 

 which project into the lumen of the gland ; they stain deeply 

 and have large active nuclei. The salivary secretion, apart 

 from the digestive properties which it has, is no doubt of 

 great importance in making the food more liquid, as is also 

 the case in the imago, and so rendering it more easy for 

 absorption. 



The Malpighian tubes (fig. 29, m. t.) arise at the junction of 

 the ventriculus and intestine in the tenth segment. A short 



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