86 PROCEEDINGS OF THE ACADEMY OF [March, 



III. THE HIND-GUT, ABDOMINAL TRACHEA AND RECTAL RES- 

 PIRATION IN THE LARVA OF MECISTOGASTER 

 MODESTUS FROM COSTA RICA. 



BY MITCHEL CARROLL. 



The abdominal viscera, including the rectum, of Mecistogaster 

 modestus have been described by Calvert (1911 b, p. 452) from a 

 dissection of larva No. 1 (male). 



The slides for the following study were loaned by Dr. Calvert 

 from his personal collection. They contain the serial transverse 

 sections of the last five abdominal segments and bases of the median 

 and right caudal gills of female larva No. 3. This larva was one of 

 those obtained by Dr. Calvert from the water collected between 

 the bases of the leaves of a Bromeliad at Juan Vifias, Costa Rica, 

 April 26, 1910 (1911 a, pp. 407-408). It was killed in hot water 

 and preserved in alcohol. Before sectioning the chitinous cuticle 

 was removed from the abdominal segments. The stains used 

 were Delafield's haematoxylin and alcoholic eosin. The sections 

 were cut .015 mm. thick. 



The Hind-Gut. 



The hind-gut may be divided into six distinct parts. A brief 

 description of these divisions is given below. 



The Malpighian tubes are attached to the gut at the junction of 

 segments VI and VII., (Calvert, 1911 h, Plate XVII, Fig. 8). From 

 this point caudad to section 35 there are twelve longitudinal folds 

 in the epithelium lining the lumen of the gut. The position of these, 

 adopting the "Clock Face Notation" of Tillyard (1916, p. 132), 

 is 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12, where the larger figures indicate 

 longer folds, the small figures shorter folds (Fig. 1 of sect. 20). 



All the figures accompanying this paper are of the larva of Mecistogaster 

 modestus Selys. 



The photographs reproduced in Figures 1-5, were made by Mr. H. A. Walters, 

 using Leitz ocular 4, objective 3. They represent the posterior surfaces of the 

 several sections. 



Fig. 1. Part of photograph of transverse section 20 (Short Intestine). 

 Enlarged 142 diameters. 



b, basement membrane. Im, bands of longitudinal muscle. 



cm, circular muscle coat of the gut. mt, Malpighian tubule. 



dim, dorsal longitudinal muscle. nc, nerve cord. 



dv, dorsal vessel. pe, pigmented epithelium. 



e, epithelial layer. rad, radial muscle strands. 



/, longitudinal epithelial fold project- ret, reticulate connective tissue. 



ing caudad into a pouch (Fig. 3). vim, ventral longitudinal muscle. 

 i, chitinous intima. 



Tracheae as in Figure 6. 



Fig. 2. Part of photograph of transverse section 55 (Prerectal Ampulla). 

 Enlarged 100 diameters. Abbreviations as in Figure 1. 



