Chap. III. HYDRACTINIA POLYCLINA. 233 



cylindrical [Figs. 1, H, l\ t, V, 2", t, and 2^, t). The walls of the tentacles {Fig. 5, t) 

 have the same relation to the walls of the body, as those of the reproductive indi- 

 viduals; the outer wall is much thinner, however, than that of the latter, but the 

 inner wall is very thick and solid, like that of Coryne and Clava, and constitutes, 

 as in these genera, a great proportion of the bulk of the tentacles. 



The proboscis of the sterile male Hydroid {Figs. 2, D, 2°, m, 2^, p, and 2'') is 

 much longer than that of the female, being rather more than twice as long as 

 the base is broad. It is composed of two walls {Fig. 2^, a b), corresponding to 

 the inner and outer walls of the body, below the head, and like it, its cavity is 

 lined with a loose layer of brownish-red granules. The proboscis of the sterile 

 Hydroid of the female colony {Fig. 1, Dp, I /»), is short and broadly conical, like 

 that of the freshwater Hydra. Whether in individuals of a male or of a female 

 colony, it has great distensibility, either swelling broadly into a great, hollow sphere, 

 with a moderate aperture {Fig. Y, m) above, or assuming a deep, saucer-shaped form 

 {Figs. V' and 1""). with inroUed rim, the lip of the mouth {m) being contorted into 

 a three, six, or seven-sided figure, or rolled outward and downward, till the bottom 

 {Figs. 1", m, and 2'', m) of its cavity is exposed. 



That there is no horny tube, closely enveloping each hydroid, as obtains with 

 Coryne, Tubularia, &c., is evident from the fact, that each individual can contract 

 and shorten itself so much as to be little longer {Fig. 2^), or no longer {Fig. V), 

 than broad. Nor is there a horny tube or cup around the hydroids, nor a secretion 

 of any sort on the upper side of the uniform layer. If we follow the outer 

 wall {Figs. 3, a, and 5, a}) of either a reproductive or a sterile individual, from the 

 base of each, we always find it terminating in a uniform, broadly spread, horizontal 

 layer {Fig. 5, a), which extends through the length and breadth of the colony. 

 Here it is much thicker, as a general thing, than the inner wall of the hydroid, 

 except where it is elevated upon the bristling spines {Fig. 6), which arise from 

 the horny network beneath, and there it varies from thick to thin, according as 

 it covers the spinules (c), or plunges between them (a), even into the interior of 

 the spine, through its lateral apertures. The inner wall of the hydroid {Figs. 3, 

 b, and 5, d) continues below, in the form of a closely anastomosing network of 

 tubes {Figs. 5, b, 6% e, b% d, Q>, b b"; PL XXVI. Fig. 18, b), imbedded in the uniform 

 layer which we have pointed out as continuous with the outer wall of the hydroid. 

 A transverse section of one of these tubes {Fig. 5", d), with the surrounding 

 uniform layer («), will give the best idea of the relation of the former to the 

 latter. The walls of these tubes are not absolutely so thick as in their upright 



the tentacles in this state, and, on this account, calls that it is the common Hydractinia echinata of the 

 the species "Clavifferum." There can be no doubt British coast. 

 VOL. IV. 30 



