NANOMIA CARA. 211 



ino- toffetlicr a community, and not a sintjle animal, as maintained ])v 

 the former. The whit ion of this question has heen considered in 

 varions Avays by Agassiz, Kolliker, Vogt, Leiickart, Gegenbaur, and 

 Huxle}-. Professor Agassiz, who was the first to show the homology 

 existing between one of these floating communities and a fixed com- 

 munity of Hydroids such as Hydractinia, has, it seems to me, given 

 the correct account of these animals. According to him, and the prin- 

 cipal points of this view have afterwards been proved independently 

 by Vogt, and also developed further, from Professor Agassiz's lectures, 

 by McCrady, a Siphonophore is neither a single animal, and its different 

 appendages simply organs, nor, according to the opposite and more 

 extreme view of Leuckart, does he push the polymorphism to such an 

 extent as to consider all the appendages, such as the tentacles and 

 scales, as independent individuals ; he compares one of these commu- 

 uities to the diflerent kinds of individuals found in a Hydractinia com- 

 munity, and thus shows beyond doubt that the Siphonophores are not 

 a natural order of the Acalephs, but simply different suborders of the 

 order of Hydroids ; the fact that they move aljout as free connnunities 

 does not separate them from the fixed Hydroids ; it would be as un- 

 natural to remove into different orders the free swimming Halcyonoids, 

 such as Renilla, Veretillum, and the fixed Gorgonia or Halcyonium. 

 It has already been fully shown Ijy Vogt that the swimming-bells of 

 Agalma and the like are only Medusas differing from the Hydroid 

 Medusae in the absence of a free proboscis and of an opening commu- 

 nicating directly with the surrounding medium. The swimming-bells 

 of Nanomia are nothing Init Medusa; having complicated chymiferous 

 tubes, remaining almost alwajs attached to the community, and per- 

 forming their part of the work. They are the locomotive individuals 

 of the community ; to them is intrusted the carrying about the whole 

 of this fraternity, while different functions belong to the other indi- 

 viduals, some of them feeding the community, others serving to repro- 

 duce it by budding, while others again reproduce it by laying eggs. 



The nature of the different kinds of polyps found along the axis 

 does not seem to have been correctly understood ; we can compare 

 them, in a general way, to the diffei'ent kinds of individuals found in 

 a Hydractinia conununity ; it seems to me that the only parts which 

 can be homologized to one of these fixed Hydroids are the fioat, the 

 original polyp, and the buds (top of Fig. 338) which drop off. These 

 are in reality the floating Hydroid, and the other individuals, developed 

 as the axis or original Hydroid l)ecomes larger, are not Polyps like the 

 original one, but Medusa? in various stages of development, having a 

 diffei'ent ajipearance from those we are accustomed to consider as such. 

 We have, in the suljordei's of 8iph()U()pliora\ connnuuities of different 

 kinds of Medusiv, instead of having counuunities of diflerent kinds of 



