Chap. II. RHIZOGETON FUSIFORMIS. 



225 



at the upper part, and there provided with ten or twelve rather thick, cylindrical, 

 tapering tentacles {t), about one third as long as the whole upright stem, which 

 is a little over one eighth of an inch high; the other form varies in outline 

 from elongate oval (A) to oval {Fi;,. 19), fusiform {Fig. 20j, short cylindrical {Fig. 

 21) or long cylindrical {Fig. 22), and springs directly upwards, like the first, from 

 the creeping tube. The interior is occupied by a long, cylindrical, hollow tube 

 {d), which bears the same relation to the other parts of the body as the proboscis 

 does to the disk of a Medusa. This is, therefore, the raedusoid form; but instead 

 of being attached to the upright hydroids of the colony, it bears the character 

 of an independent individual, like the hydroid form (B). The uniformity of the 

 red color of the group is broken by the varied colors of the medusoids, ranging 

 from dead white and light orange, through all shades, to deep orange. 



The I/^flroiik. — There is a very close resemblance between the hydroid form 

 (Fig. 17, B) of this genus and that of Clava (PL XXI. Fig. 2), especially when the 

 latter is devoid of medusas-buds (C E); but the medusae arise from the creeping 

 stolon, and not from tlie upright hydroids, as in Clava. Besides this, the hydroids 

 of the genus Rhizogeton taper uniformly from the base to the oral extremity 

 (PL XX. Fig. 17, B ill), there being no clul>shaped swelling of the upper extremity, 

 as in Clava, and a horny sheath (c c') extends up from the stolons to the base of 

 the head. At certain seasons of the year it might be very difficult to distinguish 

 the hydroids of these two genera from one another, especially if a colony of young 

 Clava (PL XXI. Figs. 5, G, and 7) should happen to be found by the side of a 

 Rhizogeton; but this is not likely to occur, for the two have very different habits; 

 the former is always found on rocks and stones in tide-pools, whilst the latter 

 invariably clings to sea-weeds, and is very much exposed to the dashing of the 

 surf We have never observed more than ten tentacles in the hydra'' of Rhi- 

 zogeton (PL XX. Fig. 17, /). These are very long and stout, quite unlike the 

 graceful, slender tentacles of Clava, and are arranged spirally on the head, which 

 comprises nearly one half of the whole height of the stem. They have a structure 

 very similar to that of Clava, both in tlie proportionate thickness of the walls 

 and in the cellular constituents; and the same may be said in regard to the 

 whole body of the hydroid, as well as the stolon (/). In regard to the size of 

 the latter we would say, however, that it is nearly as thick as the upright stems 

 of the hydroids. 



T/w JJcdii.sce-buds. — We have never seen any other than the male colony of the 

 genus Rhizogeton. As has been observed in the beginning of this section, the 

 medusa>-buds of Rhizogeton arise from the stolons, and not from the upright stems 

 of the hydroids. From the earliest period {Fig. 18), as far as we have seen, to 

 the time when the spermatic particles are discharged, they are covered by a pro- 



VOL. IV. 29 



