96 PROCEEDINGS OF THE ACADEMY OF [March, 



There are six of the radial muscle strands. They connect with 

 the rectum at the points 1, 3, 5, 7, 9, 11, of the clock notation as 

 described by Tillyard. Radiating outward they are attached at 

 their peripheral ends to the body wall. They correspond to the 

 radial rectal dilator muscles of Anisopterous larvae (Tillyard, 1916, 

 pp. 139, 140; Sadones, 1895, p. 316). 



As indicated in the above table, Tillyard in his recent excellent 

 book, The Biology of Dragonflies (1917, pp. 101, 113, 114, 115, 

 116), divides the hind-gut of Odonate larvae into two main parts, 

 the small intestine or ileum and the rectum. The small intestine 

 is subdivided into the short intestine and prerectal ampulla. The 

 first two divisions of the hind-gut in the present larva are evidentlj^ 

 homologous with these two parts. But histologically the structure 

 of this part of the intestine in Mecistogaster differs from the descrip- 

 tion given by Tillyard or the other authors mentioned above. The 

 third division of the small intestine, which is called the colon in the 

 table, is not described by Tillyard. 



Tillyard's statement (1917, footnote, p. 101) that ''in Zygopterid 

 larvae the rectum is undivided," is hardly true for Mecistogaster. 

 In the present larva, as indicated in the above table and described 

 on preceding pages, the rectum (as the term is used by Tillyard) 

 is divided into three distinct regions. These differ from one another 

 both in gross morphology and finer histological structure. 



The Trachea (Fig. 6). 



In the diagram (Fig. 6), in order to represent more clearly the 

 main trunks with their branches, most of the tracheae have been 

 drawn far laterad to their true position. The correct orientation 

 may be obtained by referring to the photographs of the transverse 

 sections (Figs. 1, 2, 3, 4, 5). The diameters of the tracheae and 

 gut have been drawn on a scale twice as great as their length. A 

 glance at Fig. 4, of section 250, shows that the rectum is slightly 

 asymmetrical with respect to the epithelial folds of the gut wall. 

 By comparing the mid-dorsal fold (No. 12) with the same fold in 

 Thaumatoneura larva (Calvert, 1915, Plate XVII) it was possible 

 to determine the true right and left sides. The latter are correctly 

 represented in the diagram. Fig. 6, showing the distribution of the 

 abdominal tracheae as seen from the dorsal side. 



From the anterior part of segment VII (Fig. 6) the two great 

 dorsal longitudinal trunks {rdt, Idt) run caudad, dorso-lateral to the 

 gut, as far as sections 40 and 60 respectively. At these points 



