Fig. 34. Diagram of a horizontal section through a gastric ostium. Fig. 35. Diagram to illustrate the formation of the central and peripheral gastro-vascular systems of a Hydromedusa (_a_, _b_, and _c_) and a Cubomedusa (_d_). Fig. 36. Vertical section through the upper part of the bell, adradial, to show horizontal vascular lamella. Fig. 37. Vertical section through the perradius, to show vascular lamella of the niche of the margin. Fig. 38. Vertical section a little to one side of the last, to show same structure. Fig. 39. Horizontal section through the upper part of the sensory niche, to show vascular lamella of the niche. Figs. 40-43. Horizontal sections through the base of a pedalium at successive levels, _w-x-y-z_, Fig. 5, to show marginal lamella. Fig. 44. Diagram to show relations of sensory niche, of bell margin and velarium in adult Tripedalia. The velarium represented as pendant. Fig. 45. To show the same structure in a young Tripedalia. Fig. 46. Horizontal section through the last just at the margin, to compare with Fig. 29. Fig. 47. Cross-section through the nerve ring. Fig. 48. The structure of the nerve as seen by focusing at successive levels. Fig. 49. Diagram to show the relation of the nerve ring to the sensory club. Fig. 50. Horizontal section through the upper part of the sensory niche, to show passage of nerve root through gelatine of subumbrella to stalk of sensory club. Fig. 51. Vertical section through base of stalk of sensory club, to show same passage. Fig. 52. Similar section to last, but nearer to perradius, to show sub-endodermal tract of nerve fibres. Fig. 53. Sensory organ in proboscis of Tripedalia, as seen from surface in living animal. Figs. 54 and 55. Sections of same sensory organ. Fig. 56. Vertical section through one side of proboscis, to show sensory organ attached to endoderm. (Tripedalia.) Fig. 57. Diagram of the outlines of sensory club seen from the side, by camera lucida. Fig. 58. Part of retina of larger complex eye cut radially. Figs. 59-62. Four sections in direct sequence through retinal cells transversely, larger eye. Fig. 63. Transverse section through the tips of cells of a slightly pigmented retina, larger eye. Figs. 64-66. Three transverse sections through vitreous body at different levels. All from same series, but not in direct sequence; larger eye. Fig. 67. Radial section through retina, to show fibres from the long pigment cells; larger eye. Fig. 68. Transverse section through vitreous body of Tripedalia near retina. Fig. 69. Vertical section through smaller complex eye. Fig. 70. Wandering cells, Charybdea. Fig. 71. Floating mass, from stomach pocket of Tripedalia. Fig. 72. Horizontal section through larger complex eye. (See text figure, p. 50.) [Illustration: CUBOMEDUSÆ. PLATE I. Gilman Drew, del. Heliotype Co., Boston.] [Illustration: CUBOMEDUSÆ. PLATE II. Conant & Crew, del. Heliotype Co., Boston.] [Illustration: CUBOMEDUSÆ. PLATE III.