NANOMIA CARA. 213 



with the exception of one root, whicli is positive, and this would repre- 

 sent the only remaining spheromere, that of the Deckstiick. 



If this view is coi-rect, it is evident that the opinion of Iluxley, who 

 considers the scale as homologous to the urn of Campanularians, can- 

 not be sustained. I have already hinted at the similarity of the em- 

 bryonic Nanomia, in the stage of Fig. 347, when it consists of only the 

 large Polj-p and the float, with the early stages of the fixed Hydrarium 

 of Melicertum, where we have at first a single Polyji, from which are 

 developed, by budding, the branches and the other kinds of individuals 

 of the community ; supposing this community, instead of fixing itself, 

 as it does, to remain moval)le, the base of the stem to expand into a 

 float and become separated from the nuiin cavity, we should have a 

 Siphonophore. The discovery by McCrady and Stimpson of the float- 

 ing Hydrarium of Nemopsis and Acaulis, where the Medusa? are closely 

 related to genera the Hydrarium of which is always fixed, reduces still 

 further the distinction which has been made of Polypi Nechali. And 

 when we find that there are genuine Medusae (Dysmorphosa) which 

 for four generations reproduce themselves by budding from the pro- 

 boscis, exactly in the same way in which we find additional individuals 

 arismg along the walls of the original Polyp among Ph_ysophorida% we 

 are at a loss to find any distinctions to separate the Siphonophores 

 from the true Hydroids, and we cannot consider them as anything 

 but floating Hydroid communities. 



Massachusetts Bay, Nahant, and Newport, R. I. (A. Agassiz). 



Cat. No. 365, Nahant, Mass., September, 1862, A. Agassiz. 



Museum Diagram, No. 27, after A. Agassiz. 



