290 Annals Entomological Society of America [Vol. Ill, 



almost completely girdles the tubule, and forces the lumen 

 toward one side, but more often the lumen is centrally located, 

 the cell completely encircling the tubule. The basement mem- 

 brane is strongly developed throughout the whole length of the 

 tubule. The chitinous intima is slightly developed in the distal 

 glandular portion, but seems to be absent in the basal portion. 

 The change from the mid-intestine to the ileum of the hind- 

 intestine is a most striking one. The large secretory cells of 

 the mid-intestine give way to the very small cells of the ileum 

 (Fig. 2() and 28, ep.) These first cells are so very small that 

 with the 1-12 immersion they appear as mere thickenings of 

 the epithelium. The nuclei are very small, deep-staining, and 

 without prominent nucleoli. A distinct, thin chitinous intima 

 is present. This thin epithelium extends caudad to a point 

 slightly before the middle of the ileum, where it develops a dis- 

 tinct fold, which extends into the lumen to form an ileal valve 

 (Fig. 2, 29 and 31 . il. v. ) From this point to the union of ileum 

 and colon, the epithelial cells are much larger, with enormous 

 nuclei, in which the small nucleoli and coarse chromatin gran- 

 ules stain deeply. The ileum is well supplied with muscles. 

 The delicate circular muscles of the mid-intestine are replaced 

 in the ileum by very strong bands which completely clothe it. 

 For a short distance, immediately behind the Malpighian ves- 

 sels, the circular muscles are absent (Figs. 28-29.) From the 

 point where the circular muscles begin, back to the ileal valve, 

 there are two layers of them. The inner layer of delicate bands 

 serves as a sphincter for the ileal valve, while the outer layer 

 is continuous throughout the hind-intestine (Figs. 29 and 3(3). 

 From the ileal valve back to the colon the individual bands of 

 the circular muscles are much stronger and more oval than those 

 of the anterior part of the ileum. The longitudinal muscles are 

 only slightly developed in the hind-intestine. From longitu- 

 dinal sections it would appear that, at the point where the first 

 circular muscles appear, the longitudinal muscles divide to 

 form an inner and an outer layer, but from cross sections only 

 outer longitudinal muscles appear in front of the ileal valve. 

 Three strong, and two or three smaller strands appear clustered 

 together along either side of the canal. From the ileal valve 

 to the colon these same lateral clusters of outer longitudinal 

 muscles appear as well as scattered inner strands between the 

 circular muscles and epithelium (Fig. 32, 1. m.) 



