18 



organ at least) being transverse ; owing to this circumstance the ten- 

 tacles, when partially extended, present the appearance of transverse 

 compartments. 



In the centre of the substance of the bulb there is a cavity 

 which communicates, I believe, above with the marginal canal, and 

 is continuous inferiorly with a tubular cavity in the centre of the 

 tentacle. The immediate walls of the cavity in the bulb are formed 

 of cells, having brownish coloured granular contents, and which I 

 consequently presume are of a glandular nature, and to the presence 

 of which cells is due the upper elongated brownish spot (a, fig. 12) 

 mentioned above. The lower, circular, crimson spot is composed of 

 tolerably uniform, coloured corpuscles or pigment grains, which seem 

 to be lodged in the outer cells of the parenchyma, or between the pa- 

 renchyma and the basement membrane of the bulb. It is, I believe, 

 this assemblage of coloured granules that has been dignified with the 

 name of " ocellus," though it seems to present few of the characters 

 of a visual organ. The exterior of the bulb is covered with a thick 

 layer of cells, each of which contains, or rather partially surrounds, 

 one of the peculiar spiculiferous or filiferous vesicles, common in all 

 the Hydra, hydroid Polypes, Actinia, &c. On the tentacles them- 

 selves, these filiferous vesicles lose, or come out of, their parent cell, 

 and assume the aspect under which they more commonly occur. In 

 this form they exist, scattered more or less irregularly throughout 

 the whole length of the tentacle, being, of course, more closely or 

 more rarely set, according to the degree of extension of that organ. 

 The marginal and four radiating gastro -vascular canals are all con- 

 stituted in the same way. They appear to have a distinct but very 

 delicate wall or basement membrane, which is lined by an epithelial 

 layer of elongated cells (d, fig. 8) with large granular nuclei, and pro- 

 bably of a secretory or glandular nature. On the exterior of the 

 basement membrane there are also placed similar cells, but not so 

 closely arranged. Ciliary motion is evident throughout these canals, 

 but the cilia themselves are inconspicuous. The fluid which circu- 

 lates with considerable rapidity in these canals, carries along with it 

 numerous corpuscles, mostly granular and of various sizes. The 

 four gastro-vascular canals open directly into the marginal canal, and 

 superiorly they penetrate the base of the peduncle. Soon after the 

 entrance into the base of the peduncle (c, fig. 1), they become 

 narrower, and appear to lose their distinct, defined wall or base- 

 ment membrane, and to become mere channels between the cells, 

 constituting the substance of the base of the peduncle presently to 



