256 DE M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 



able size, and in the living animal undergo various changes in shape by pres- 

 sure against each other, the body-wall and viscera of the worm. On extrusion 

 into the surrounding water they become very transparent, and their broken 

 contained granules collect together at one point (Plate X. fig. 1). Tincture 

 of iodine and chromic acid colour them deep yellow, while sulphuric ether 

 does not materially affect them. Dilute glycerine first corrugates, and then 

 causes them to burst, giving exit to the contained clear granules (Plate IX. 

 fig. 7), which measure about e-oVoth of an inch in diameter. Some of the 

 corpuscles are smaller, and their contained granules less in proportion. Besides 

 the foregoing, there are many elliptical, curved, and granular corpuscles (Plate 

 IX. fig. 8) in the perivisceral space. In the elongated form the perivisceral 

 corpuscles are less conspicuous both as regards number and size. The larger 

 bodies in this case are rounded cells (Plate IX. fig. 9), filled with much more 

 minute granules than in the preceding form, and many show a granular nucleus. 

 The other corpuscules (Plate IX. fig. 10) are elliptical or fusiform, flattened, trans- 

 parent and non-granular, and often longer than the diameter of the ordinary 

 granular corpuscle just described. As contrasted with a gland-cell from the 

 intestinal wall, the perivisceral corpuscle in the former case is widely different, 

 while in this it has much smaller granules, is pale, and easily distinguished from 

 the other with its highly refracting yellowish granules. In a form occurring 

 abundantly in certain lakes with the latter, and referable to M. Claparede's 

 genus Limnodrilus, the perivisceral corpuscles are remarkably developed. They 

 are larger than usual, very transparent, and frequently show a somewhat 

 puckered outline within the body of the worm. They also have the peculiarity 

 of adhering here and there in considerable numbers to the intestinal coating. 

 Few or none of the ordinary fusiform or other bodies are present. On ex- 

 truding these corpuscles into the water they swell out, and show a large 

 granular nucleus, the rest of the cell being quite translucent. Moreover, both 

 cells and nuclei have a nearly uniform diameter throughout the fluid. On con- 

 trasting these corpuscles (Plate IX. fig. 11) with the gland-cells from the 

 intestine (Plate IX. fig. 12), a very marked difference is observable. The for- 

 mer are quite transparent — with the exception of the nucleus, becoming slightly 

 granular only after remaining many hours in the water. They have nuclei 

 of definite size and structure, which retain their shape and appearance after the 

 bursting of the cell-wall. Acetic acid and ether only show the structure just 

 described more clearly. On the other hand, I have watched the gland-cells 

 from the intestine under water and various reagents side by side with the others, 

 and for a considerable time; but I do not feel able to say that nuclei or 

 other contents than the refracting granules have been detected. The gland-cell 

 may be set in motion, rolling over and over, so as to expose it all round, yet 

 not a trace of a nucleus is seen. In all the forms there is thus a considerable 





