268 Annals Entomological Society of America [Vol. XV, 



When retracted these gills lie within the rectum, which serves a 

 double function, with their distal ends or tips close to the anus and just 

 barely within the aperture. They may function slightly at this 

 time. 



In surface view the gills present a cylindrical form which tapers as it 

 extends distally. Upon the surface are transverse ridges which are 

 bounded by thread-like depressions. These depressions are as deep as 

 the ridges are wide, for these ridges are made up of rings of cells one 

 cell deep and one cell wide. At rest these cells are cubical, being as 

 deep as they are wide, and the depressions are the expansion spaces 

 between the cells. In expansion this ring of cells becomes narrower 

 in diameter and the cells themselves wider and more shallow. Compare 

 Plate XVII, Fig. 6, where the gill is at rest, and Fig. 7, where it is in 

 extended condition. The tips of the gills are more dense and of a darker 

 color than the rest of the gill. This condition is due, no doubt, to their 

 close proximity to the anal aperture and to the fact that they must at 

 times push their way through waste material in their extension. 



To get a clear conception of the formation of these gills, it is necessary 

 to start with their origin in the wall of the intestine in the ninth segment. 

 Here the glandular large celled condition of the intestinal wall ceases 

 and becomes cubical. The wall is thin and the six longitudinal folds 

 extend inward so as to form a semi-valve at the head of the rectum, 

 Plate XVII, Fig. 4. Gradually these folds merge into four and form the 

 four gills. Plate XVII. Fig. 5, shows these longitudinal folds merging 

 into the gills and being continuous with them. After the formation 

 of the gill the rectal wall does not again fold, but passes directly to 

 the anus. 



At rest the width of the gill is about one-third its length, which 

 normally is slightly less than the width of the ninth segment. The gill 

 is capable of extension to about three times its normal length, and at 

 this time the wall becomes thin and the cells much longer than deep. 

 Not all of this extension length is made by the gill itself, as the folds at 

 the head of the rectum extend and the caudal wall of the rectum itself 

 is carried down with the gills, Plate XVII, Fig. 7. 



The deep cells of the walls of the gills are possessed of large nuclei 

 and are glandular in appearance. These cells take up about four- 

 fifths of the diameter of the gill when at rest, leaving the other fifth 

 for the muscle which extends from the conjunctiva of the lateral and 

 ventral walls between segments eight and nine. Each gill possesses a 

 muscle which arises at a corresponding place upon the conjunctiva 

 and extends to the tip of the gill. Each gill muscle is three branched, 

 Plate XVII, Fig. 8, and when at rest lines the gill. The gills are covered 

 with a very thin intima, which is continuous with that of the rectum 

 and intestine. 



GLANDS. 



Not all the glands in the body of the trichopterous larvae are con- 

 sidered here. The writer has confined her attention to the silk glands, 

 the thoracic glands and the glands in the head, in this last only those in 

 L. indivisus have been studied. 



