Chap. II. MORPHOLOGY AND NOMENCLATURE. 81 



viduals of one ami the same communit}- are by no means so uniform among them- 

 selves as ua the class of Polyps. The Acalephian connnnnities are, indeed, generally 

 23ol3^morplious, and cases of great uniformity among their individuals are rare. For 

 these communities Ave need comprehensive names, as much as for the Polyp 

 communities. Now, just as the name Pohjparhna lias l)een framed to designate a 

 Pohjp comnmniti], we may apply the name of Ili/drarmm to a community of combined 

 Hi/drce. In this sense, a bunch of Corynas or of Tubularia) iniited by their stems 

 and stolons, a patch of Hydractinioe rising from their common basis, a branching 

 Campauularia or a Laomedea communicating Avith others by stolons, or eA'en a 

 single stem Avith its lateral buds, constitutes ILjdraria. And so also are Sertularia? 

 and Plumularia? genuine Ilijdrcwia. The same name must also apph' to the Siphono- 

 phor£e as far as they are communities. But here a distinction is at once suggested, 

 iu accordance with the special character of the indiAaduals forming these communities. 

 As long as the combined individuals are all Il^-dra^, the name Hydrarium correctly 

 applies ; but among Siphonophora?, as among Corynoids and Tubularioids, there 

 arise Meduste buds from the Hydra^, and these Ijuds are either single, or form by 

 themselves communities of individuals in no Avay to Ije distinguished from genuine 

 Medusae, to w'hich the name of Hydraria cannot )je applied, but for which that 

 of Medusarium seems very appropriate. I would therefore call 3Iedusamim every 

 buuch of Medusae buds arising from a Hydra, in contradistinction to the single 

 Medusaj buds produced hj other kinds of Hydra^. For instance, the Hydraj of 

 a Coryne Hydrarium never produce 3Iedusaria, but always single Medusa) buds, 

 while the Hydra; of a Tubularia H^-drariiun ahvays produce Medmaria. The 

 structural combinations in these animals ai'e so complicated, that, unless Ave make 

 these distinctions, it Avill become necessary to resort to long circumlocutions correctly 

 to describe them, and duly to discriminate the true nature of the diflerent kinds of 

 indiA-iduals united in one and the same community. It is eA^ident, that a Tubularia 

 community, so long as it produces no Medusa? buds, is simply a Hydrarium ; but 

 presently it brings forth Meduste buds in large clusters, hanging from the single 

 Hydras in the form of Medusaria, and each Hj^dra produces several such Medusaria, 

 Avhich are as much parts of the enlarged community as the single Hydra; them- 

 seh'es. By this time the community is no longer a mere Ilydrarimn, but a Hydrarium 

 bearing Medusaria. It is noAv a community of heterogeneous communities, Avhicli 

 may well be called a Ilydro-Mcdumrium. 



The use of such names for these different communities and their combinations 

 win greatly simplify our descriptions, and add much precision to our characteristics 

 of the different families and genera of the Hydroids. For instance, the Tuhdarioids 

 as a family ma}' Ijc described as II//dro-3Iedusaria arising from single IL/drw Avhich 

 by budding and by stolons become Ilijdraria ; each adult Hydra producing in time 



