90 PROCEEDINGS OF THE ACADEMY OF [March, 



sopterous larvae (Sadones, 1895, pp. 280, 295; Tillyard, 1916, p. 131 

 and 1917, pp. 101, 113, 114), but the character of the epithelium 

 does not correspond to that described by Tillyard and Sadones. 

 The latter describes and figures two lateral plates of thick epithelium 

 separated from one another by numerous folds of thin epithelium. 

 In this portion of the Mecistogaster intestine there is only one kind 

 of epithelium. In the larva under discussion it is not very well 

 preserved, but seems to be similar to that already described as 

 cccurring in the first and third divisions of the hind-gut. Then, 

 too, there is no narrowing or constriction of the intestine posterior 

 to this pouched or csecal region as in the other insects mentioned 

 above; the pouched region passes without any very apparent change 

 in diameter into the rectum. 



In the diagram (Fig. 6), the gut between sections 50 and 80 (the 

 part which, as has been suggested, is probably homologous with the 

 prerectal ampulla of other insects) is seen to be supplied with branches 

 from the left and right visceral tracheae (Ivs, rvs). Some of these 

 tracheoles end just within and some, just without, the basement 

 membrane of the large columnar cells of the three broad folds (4, 

 8 and 12) or bands referred to above. The mid-dorsal (12) and the 

 left ventro-lateral (8) folds are supplied by tracheoles from the left 

 visceral trachea (Ivs); the right ventro-lateral fold (4) is supplied 

 by branches from the right visceral trachea (rvs). No tracheoles 

 have been found penetrating any of the other folds of the gut 

 epithelium thus far mentioned. 



The next, or fifth, division of the posterior intestine is the rectum 

 proper. (Minot, 1880, pp. 209, 210, 218; Packard, p. 318; Tillyard, 

 1916, pp. 131, 140-189 and 1917, pp. 101, 114, 115, 116; Sadones, 

 1895, pp. 277, 280, 294-315; Faussek, 1887, pp. 708-711; Bordas, 

 1898, pp. 48, 52.) In Anisopterous larvae it is this region which 

 functions as the branchial basket (Tillyard). In Mecistogaster there 

 is, of course, nothing corresponding to a branchial basket. The 

 so-called rectal glands, which Tillyard (1916, pp. 179-189) has 

 shown to be homologous with the rectal gills, are represented by 

 thr^e broad longitudinal folds of thick columnar epithelium (Fig. 

 4 of sect. 250), instead of six as in Anisopterous larvae. These 

 folds occupy the same relative positions (Nos. 4, 8 and 12, of the 



Fig. 3. Part of photograph of transverse section 150 (Pouched Part of the 

 Rectum). Enlarged 115 diameters. Abbreviations as in Figure 1. 



Fig. 4. Part of photograph of transverse section 250 (Rectum). Enlarged 

 114 diameters. Abbreviations as in Figure 1. 



