1922] Branch: Internal Anatomy of Trichoptera 269 



The Silk Glands: Of all the glands of the trichopterous larvae 

 these are the most prominent. They practically fill the part of the 

 body cavity not occupied by the alimentary canal and extend from the 

 labial spinneret into the seventh segment. They are opaquely white, 

 having a pinkish cast in a fresh specimen. Their content is sticky and 

 if the glands of a fresh specimen be broken in dissection the secretion 

 will so glue the organs and tissues together as to make further dissection 

 impossible. This difficulty is remedied by applying Gilson's preserva- 

 tive' to the freshly opened specimen and allowing it to remain for fifteen 

 or twenty minutes. 



Upon the floor and in the center of the anterior edge of the labium 

 is a spinneret, Plate XVIII, Fig. 3, at sp. This is connected to a single 

 tube of .2 mm. in length. In this region is the silk press composed of 

 muscles which control the flow of secretion. This structure does not 

 differ from the structure of the forms studied by Gilson, 1894, and needs 

 no further discussion in this paper. At the posterior margin of the 

 labium this single, slender tube becomes divided into two and passes 

 ventrad of the nerves extending from the sub-oesophageal ganglion to 

 the mouth parts. On reaching the ganglion each member of the pair 

 of tubes passes laterad of the ganglion, Plate XVIII, Fig. 4, and then 

 approaches its mate and passes with it underneath the oesophagus. At 

 the posterior margin of the sub-oesophageal ganglion the tubes change 

 their character from that of a duct to a true gland. In the duct the 

 cells are small with simple nuclei. Externally the change is marked 

 with a depression as though a thread were fastened tightly around the 

 tube. Back of this depression is the gland proper, composed of an 

 outer wall with an irregularly shaped nucleus in a flattened cell. This 

 outer wall is two cells, in circumference, the cells are hexagonal with 

 the lateral face in a triangle. The front face of the triangle meets 

 the posterior face of the triangular side of the other cell, see Plate 

 XVIII, Fig. 5. Inside of this wall, which is frequently very loosely 

 applied, is the inner tube consisting of a firm cylindrical wall, where 

 the secretion is formed and inside of this heavy wall is a narrow tube 

 through which the secretion passes to the duct, Plate XVIII, Figs. 

 6 and 6a. 



These silk glands lie ventrad of the alimentary canal throughout the 

 thorax and frequently as far as the second abdominal segment. Finally 

 they make their appearance at the sides of the alimentary canal and 

 increase in size. They extend to the sixth segment where they turn 

 forward again and extend to the second and third abdominal segment, 

 turning backward they reach to the seventh segment where the distal 

 ends are frequently folded under the intestine or float free among the 

 various folds of the Malpighian tubules, Plate XV, Fig. 1. For a 

 detailed description of these glands see Vorhies, 1908. 



Thoracic glands: Gilson, 1896, shows Phryganea grandis as possess- 

 ing three glands or pairs of glands in the thorax, one pair to each of the 

 segments. These glands are formed of small tubes which come together 

 to form a small reservoir from which a single tube extends. This tube 

 meets its fellow and together as one tube they open to the exterior in a 

 small pore. Henseval, 1895-6, did not find the three pairs in all of the 



