186 HYDROID.E. Part IV. 



nothing can be more graceful than the manifold curves and waving lines caused 

 by the motion of the branches and tentacles of this little animal. A community 

 of Coryne mirabilis resembles, somewhat, a tuft of moss (Vol. III. PI. XVII. Fig. 1). 

 It attaches itself to almost any thing that comes in its way, whether it be a shell, 

 stone, searweed, or a log, and may be found either in pure sea-water, or at the 

 mouths of rivers Avhere there is more or less brackish water. It does not seem 

 to be dependent upon the purity and cleanliness of the water, if it is kept in 

 constant agitation by the ebb and flow of the tide. It is not known by what 

 means the Hydroid attaches itself to any object on which it rests; probably, how- 

 ever, by a kind of agglutination, at the time when the horny sheath of the young 

 is forming. There is no distinct stoloniferous, or creeping portion, apart from the 

 upright branches, such as exists in Campanularians. The stem creeps as far as it 

 can find support, throwing up here and there a minor branch, and then launches out 

 freely, becoming all the more irregular in its divisions, for want of a definite point 

 of attachment, and diverging in every possible direction around an imaginary axis. 

 There does not appear to be any regularity in the mode of branching of the stem, 

 nor any particular angle at which the branches diverge from each other. It is 

 seldom, however, that angles of more than sixtj^ or seventy degrees intervene 

 between any two branches. 



A colony of these hydroids may be described as an irregularly branching tube, 

 with club-shaped terminations, commonly called the head, open at the summit, each 

 one of which bears a number of scattered, spirally arranged, tentacles, with glob- 

 ular tips (PI. XVII. Fiys. 1 and 1"). In the spring and autumn, the general appear- 

 ance of the club-shaped termination is modified by the presence of more or less 

 globular expansions (PI. XVII. Fiys. 2, m md, 3, a, 5, a a, and 9, md), of various 

 sizes, either intermixed with the tentacles, or on the neck, just below them. These 

 spheroid bodies are the alternate Medusa generation, budding from the heads of 

 the Hydroids, Avhile the Hydroids themselves are developed from the eggs of the 

 free Medusse. Every such organically connected Hydroid community is either male 

 or female ; or, without insisting upon the sexuality of the hydroid form, we may 

 say that every colony bears either only male or only female Meduste. The club- 

 shaped head may assume an infinite variety of forms, changing, successively, from 

 an exceedingly elongated cylindrical shape (PI. XVII. Fig. 12) to shorter .and shorter 

 proportions (PI. XVII. Figs. 4, 11, 3, 5, 2, 6, and 9) ; or it may be very much 

 inflated at times {Fig. 6), showing, indeed, as gi-eat a power of extending and 

 contracting as the Actinioids, and perhajis a greater diversity of forms. Below the 

 head, the stem is rather constant in form, being restrained by the rigid, horn}' 

 sheath (PI. XVII. Figs. 11, c, and 15, c, and PL XX. Fig. 2, c). The whole com- 

 munity, from the base to the tip of the club-shaped terminations of the branches, 



