266 DR M'INTOSH ON SOME POINTS IN THE STRUCTURE OF TUBIFEX. 



of trumpet-shaped organs, one on each side anteriorly. When empty the sacs 

 have a somewhat coarse granular appearance, and do not show the rolling 

 contractions. 



In a specimen with largely developed ovaries, a curious ovoid organ (Plate 

 X. fig. 13) occurred at the anterior part of the eleventh segment, and another 

 at the anterior part of the twelfth. Externally there was a dense capsule, and 

 internally a minutely granular mass altogether different in appearance from the 

 structure of the ovaries or their contents. They measured about ^th to r^th 

 of an inch in diameter, and were of so unyielding a nature that they soon 

 escaped by rupture through the body-wall of the worm. 



EXPLANATION OF THE PLATES. 

 Plate IX. 



Figure 1. Bristle and dorsal hook of Tubifex rivulorum, from the anterior segments. x 350 diam. 

 Figure 2. Ventral hooks of the same species. x 350 diam. 



Figure 3. Anterior hooks (accompanyingthe bristles) of the elongated form from the lakes ; a, pro- 

 cesses in the fork. x 350 diam. 

 Figure 4. Body-wall (a) of T. rivulorum, with parasitic Vorticellae. x 210 diam. 

 Figure 5. One of the parasitic Vorticellas in a partially expanded state. x 350 diam. 

 Figure 6. Perivisceral corpuscles of T. rivulorum ; a, cells in the ordinary condition; b, a cell from 



the perivisceral chamber after the addition of chloroform ; c and d, the contents of the 



latter more highly magnified. In all probability, however, this (b) is only a sperm-cell in 



course of development. x 350 diam. 

 Figure 7. The same after the action of dilute glycerine, with extruded clear granules. x 350 



diam. 

 Figure 8. Variously shaped corpuscles from the perivisceral fluid. x 350 diam. 

 Figure 9. Perivisceral corpuscles of the elongated Tubifex from the lakes. x 280 diam. 

 Figure 10. Elliptical and other corpuscles from the same fluid. x 350 diam. 

 Figure 11. Perivisceral corpuscles of a species referable to Clap arede's genus Limnodrilus. x 850 



diam. 

 Figure 12. Gland-cells from the intestinal wall of the same species. x 350 diam. 

 Figure 13. Ciliated epithelial cell from the interior of the digestive tract of the same animal. x 850 



diam. 

 Figure 14. a, b, c, d. Various forms of the Opalina parasitic in the alimentary chamber ; b represents 



an outline of the anterior end of a large specimen, the cilia being omitted, x 210 diam. 

 Figure 15. Parasitic Nematode worm from the same region. x 400 diam. 

 Figure 16. Anterior region of the elongated Tubifex from the lakes, showing the dense coiling of the 



blood-vessels anteriorly in the semi-contracted condition ; a, dorsal blood-vessel ; d, 



ventral. 

 Figure 17. Anterior segments of Tubifex rivulorum in a somewhat contracted and flattened condition, 



exhibiting the arrangement of the , vascular system ; a, fissure at the mouth ; d, dorsal 



blood-vessel ; v, ventral. The figures indicate the segments. 

 Figure 1 8. Segmental organ of the same species from behind the middle region of the bod}- ; a, the 



septum. 

 Figure 19. Sperm-cell in the granular stage. x 350 diam. 

 Figure 20. Awl-shaped bodies and granules from a sperm-cell in course of development. x 400 



diam. 

 Figure 21. Spermatozoa of T. rivulorum. x 350 diam. 



