66 W. G. RIDEWOOD. 



FIGS. 16, 17, 18, 19, 20. Views of the ostia and spines of Gephalodiscus (Demiothecia) hodgsoni. Many 



of the spines are standing out obliquely towards the observer. Nat. size. 

 FIG. 21. A forked spine of C. hodgsoni showing the mode of growth, (x 7.) 



FIG. 22. Diagrammatic representation of the cavity of the tubarium of C. hodgsoni, as though the 

 polypides had been removed, a cast made of the interior, and the test subsequently stripped off. 

 Nat. size. 



PLATE 5. 



FIG. 23 A flattened plume of Cephalodiscus (Idiothecia) nigrescens in moderate contraction, seen from 



the central (neural) aspect. Note the rounded extremity of the axis, (x 50.) 

 FIG. 24. A plume in moderate extension. Note the pointed extremity of the axis. ( x 50.) 

 FIG. 25. Usual aspect presented by contracted plumes, when seen from the side, (x 50.) 

 FIG. 26. Another plume seen from the side, with the axis less strongly curved, (x 50.) 

 FIG. 27. Another plume in side view. Note that in this plume, apparently fully-grown, the pinnules 



are few, and the distal ones project beyond the extremity of the axis, whereas in the plumes 



shown in figs. 25 and 26 they fall considerably short of it. (x 50.) 

 FIG. 28. Transverse section of a plume-axis of 0. nigrescens taken at about one-third of its length 



from the free end. (x 160.) b.v., blood-vessel ; c.e., ciliated epithelium ; m., muscle ; 



n.t., nerve tract ; p.e., pigmented epithelium ; s.Jc., skeletal layer. 

 FlG. 29. Transverse section of a pinnule of C. nigrescens. (x 420.) 

 FIG. 30. A similar section passing through a pigmented cell, (x 420.) 

 FIG. 31. A plume of Cephalodiscus (Demiothecia) hodgsoni seen from the side, (x 40.) The pinnules 



of the farther side are not shown. 



FIG. 32. A plume of C. hodgsoni seen from the aponeural aspect. ( x 40.) 

 FIGS. 33, 34, 35, 36. Terminal portions of plumes of C. hodgsoni in optical section, showing the 



refractive globules projecting beyond the surface of the terminal bulb, (x 140.) Note that 



in fig. 36 the most distal pinnule arises from the end-bulb itself, whereas more usually it 



arises from the neck of the bulb. 

 FIG. 37. Testis of Cephalodiscus nigrescens dissected out and viewed as a solid object by reflected light. 



(X 50.) 

 FIGS. 38, 39, 40. Ovaries of C. nigrescens dissected out and viewed by transmitted light after mounting 



in diluted glycerine. (X 50.) 

 FIG. 41. --Testis of Cephalodiscus hodgsoni as seen by transmitted light after mounting in diluted 



glycerine. ( x 40.) 

 FIG. 42. Ovary of C. hodgsoni by transmitted light, (x 40.) This was the largest ovary found. 



The relative opacity of the two largest ova is due to yolk. 

 FIGS. 43, 44, 45, 46. Ovaries of C. hodgsoni showing differences in the distribution of the red pigment. 



(X 40.) 

 FIG. 47. The ovary and testis of a hermaphrodite polypide of G. hodgsoni. (x 40.) Note that the 



testis duct has red pigment, which is exceptional, (cf. fig. 41.) 



PLATE 6. 



FIG. 48. Egg of Cephalodiscus (Demiothecia) hodgsoni. (x 40.) 



FIG. 49. Polypide of C. hodgsoni seen from the side. ( X 28.) Letters as in fig. 7, pi. 3. 



FIG. 50. A polypide of G. hodgsoni with longer stolon than the last, and a flatter shield : ventral view. 



(X 28.) 



FIG. 51. Side view of a polypide of G. hodgsoni with a well-extended stolon, (x 28.) 

 FIG. 52. A long-stalked plumeless polypide of C. hodgsoni. (x 16.) 

 FIG. 53. The post-oral lamella of a polypide of C. hodgsoni dissected off and flattened out ; dorsal 



view, (x 40.) 



FIG. 51. Young bud of C. hodgsoni. (x GO.) 

 FIG. 55. Later bud, with first pair of plume-axes appearing ; dorsal view. ( X GO.) 



