1911] Watson: The Genus Gyrocotyle. 407 



mens which had begun to decay in the intestines, and in prepara- 

 tions made by Von Rath's method, a perfectly definite and 

 clearly marked operculum was found (operc., pi. 38, figs. 38, 39, 

 40). This does not appear to be comparable to the operculum 

 figured by Haswell (see my plate 47, figure 81)*. Its margins are 

 finely toothed, and the shell is somewhat thinner in the opercular 

 cap than elsewhere. 



VI. EXCRETORY SYSTEM. 



The network of excretory canals, so richly developed in 

 Gyrocotyle, is one of the first features to strike the eye in obser- 

 vation of the living animal. Wagener (1851) saw and described 

 it, and noted particularly its wonderfully elaborate development. 

 The excretory system consists of the following parts : ( 1 ) " flame- 

 cells, " (2) capillaries, (3) excretory canals distributed outside 

 the inner longitudinal muscle layer, (4) excretory canals lying 

 within and among the fibres of the inner longitudinal muscles. 



The "flame-cells" (pi. 43, figs. 62, 63) are large, with swollen 

 base in which lies an oval nucleus with rich, deeply-staining 

 chromatin reticulum. The surrounding cytoplasm is granular, 

 occasionally vacuolated, and stains as heavily as does that of the 

 gland-cells. Running apparently from the apex of the nucleus is 

 a fine thread, extending for some distance through the hollowed- 

 out body of the cell. Each flame-cell thus forms an intracellular 

 canal, which leads into a capillary. These flame-cells are found 

 only in the outer layers of the body in what has been described 

 as the "intermediate" region, within the subcuticular layers and 

 outside the inner longitudinal muscle mass. Neither Spencer 

 (1889) nor Wagener (1852) found any such structures; Lonn- 

 berg (1891) found them, but tells us nothing about them, except 

 that they lie in the " Rinden-schicht. " 



The capillaries are the fine tubules into which the intra- 

 cellular ducts of the flame-cells lead. They have very thin walls, 

 and differ from the excretory canals in not having a cuticular 

 lining or a muscle layer. They are found throughout the body 

 wherever flame-cells appear. 



The excretory canals lying outside the inner longitudinal 

 muscle mass differ from those lying within this layer chiefly in 



