210 NAXOMIA CARA. 



diiferent kinds of individuals taking the place we find them occupying 

 in the adult ; the swimming-bells are placed immediately under the 

 float, and the polyps between them and the primitive polyp. The 

 protecting scales increase rapidly, and in Fig. 350 we have a .voung 

 JS'anomia having two well-developed polyjjs, as man}^ scales, and as 

 many tentacles, one of the polyps being the first terminal one, and 

 the other a lateral polyp, at the base of which are found the rudi- 

 mentary tentacles, while immediately under the float we find a cluster 

 of rudimentary swimming-bells, as for developed as those of Fig. 337. 



From this point there is no doubt that we have before us a young 

 Nanomia, and the future phases of the development are only changes 

 of quantity. The various members of the community have, however, 

 a very different degree of development. What is particularly charac- 

 teristic of the young Nanomia is that it is entirely composed of the 

 polyp element, and of the polyps with knobbed appendages ; it is only 

 somewhat later that the scales make their appearance, and we then 

 have a sufficient number of these polyps added to make quite an exten- 

 sive community before any other kind is formed, and before the swim- 

 ming-bells are developed. We generally find a couple of large swim- 

 ming-bells preceding the appearance of the second kind of polyp (Fig. 

 339) ; it is not till still later that the Hydrocysts (Fig. 341), as Huxley 

 has called the closed polyps, make their appearance. The remaining 

 swimming-bells are slow in their development ; we do not usually find 

 more than two in quite large specimens, and it is only in the adult, 

 where we find the buds which are to separate as young floats and 

 where the sexual individuals have begun to make their appearance, 

 that there are from four to six swimming-bells. (Fig. 332.) 



From this slight sketch of the order of succession of the diflerent 

 individuals, we have the means of dividing all the Siphonophores into 

 three great suborders, according to the degree of development of the 

 three principal elements. Lowest are those in which the float has the 

 greatest predominance, and in which the different individuals of the 

 community appear as secondary appendages, such as Porpita, Velella, 

 and Physalia ; in the second suborder we have the various stages of 

 combinations of the hydrarium and the swimming-bell elements, in the 

 following forms, — Rhisophyza, Apolemia, Agalma, Nanomia, Halistem- 

 ma, Stephanomia, and Forskalia ; while in the third and highest sub- 

 order we find the greatest development of the swinnning-l)ells, accom- 

 panied by a reduction in the number of individuals forming a single 

 community, and a further specialization of parts not found in the 

 preceding orders. The different appendages which are found along 

 the axis of these floating Hydroids have been considered by most 

 English investigators as simple organs, while the greater number of 

 German writers believe them to be diflerent kinds of individuals, form- 



