Fernald has described a process of regeneration which 

 takes phice iu the mid-gut cells, but it has not been possible 

 to conhrm his observations with any degree of certainty. 

 He remarks that ''The nuclei of the epithelium divide, and 

 one of the two that are thus formed in each cell passes 

 towards the free face of the cell, while the other passes 

 towards its base. The cells' walls now become indistinct 

 and delaminatiou occurs, the outer half of each cell being 

 thrown off. These moulted cells collect in the lumen of 

 the gut, and remain there until the chitin of the 

 remainder of the body is thrown off, when this is also 

 removed from the body. The outer edges of the cells 

 remaining- form a new * Harchensaum/ and resume 

 their normal condition '' (8. p. 455). A somewhat similar 

 process of moulting or regeneration of the mid-gut cells 

 has been described b}' Sommer in Tomocerus i^M acrutouxa) 

 (23), and by Prowazek in Isotoma (21). 



The musculature of the mid-gut consists of two layers, 

 an outer longitudinal and an inner circular set (Plate \ ., 

 fig. 49, and Plate YI., hg. (jl). The circular hbres each 

 consist of a single greatly elongated cell, the opposite ends 

 of which meet in the mid-dorsal line. Previous to uniting, 

 the two ends of each fibre break up into their component 

 fibrillse or sarcostjdes, and also receive contributions from 

 adjacent fibres (Plate YL, fig. 61). The longitudinal 

 fibres consist of greatly elongated cells placed end to end. 

 The nuclei of both the circular and longitudinal fibres are 

 hard to detect ; they are very minute, and those of the 

 circular muscles are principally dorsal in position. A 

 fine membrane of connective tissue closely invests the 

 outer surface of the muscle fibres, and also lines the 

 rectangular spaces enclosed between them (fig. 30). 

 Where the mid-gut joins the hind-gut its epithelium 

 becomes greatly thickened, and forms a ring-like bulging 



