Chap. II. THE DIFFERENT RADIATA. 57 



synonyms, the swimming-bells are boat-shaped, and their radiating tubes winding, 

 as in Galeolaria among the Diphyidte. In the genus Athorybia, the swimming- 

 bells have the shape of arehed ribs ; and, though no radiating tuljes have 

 been described in them, I doubt not that they will be found, unless there 

 exist here, as in Tubularia, various combinations of the more Hydroid or more 

 Medusoid features. In the genus Apolemia, the swimming-bells resemble those of 

 Physophora, and the Hydroids are arranged in clusters, hanging at intervals, along 

 the main axis. 



The genus Physophora, with its double row of bottle-shaped swinnning-bells, 

 approaches more nearly Ilippopodius and Vogtia than Agalmopsis and Forskaliaj for 

 the sucker-like Hydrae are few [Fig. 38), at the base of the axis, as in Yogtia, 

 and the Medusae buds form small bunches. In Agalmopsis, ^. ^^ 



on the contrary, there is below the douljle row of heart- 

 shaped swimming-l)ells a long string of large Hydroids, pro- 

 vided with protecting scales and furnished with tentacles, 

 and their sexual Medusa) buds form small bunches, suspended 

 at consideralde intervals between them. In Forskfdia, finally, 

 the more or less quadrangular swimming-bells, arranged in 

 several rows, form a long cone, from w'hicli hang two kinds 

 of Hydroids, one protected by, and the other without, scales; young PnysonioRA, 



■^ ' -^ "^ ' _ ( Ciipkd from Gegenbauer.) 



and it is from the cluster of the latter that arise the male « Buds of swimming bcns.- 6 6 so- 



^ ATI 11 called tentacles ; lower b so called 



and female Medusa? buds. poiyp. — cc Feelers with lasso 



It is plain, from this rapid survey of the Siphonophora?, 

 that, with the exception of Physalia, Vellella, and Porpita, which consist of Hydroids 

 only, they all agree in having a set of more or less numerous Medus;x!-like Hy- 

 droids at the base of their common axis; and that from the prolongation of this 

 axis arise other Hydroids, either altogether resembling the common Hydroids, without 

 a bell, or protected )jy a scale-like open bell, in a measure intermediate between 

 Medusae and Hydroids; and that, finally, all produce Meduste buds. These Medusae 

 buds mostly wither upon the community, though in some they free themselves in 

 the shape of twin individuals composed of a Hydroid and a Medusa, which have 

 been described as distinct genera, under the names of Eudoxia, Aglaisma, etc. 



It follows from all this, that while the Siphonophorte must be united with the 

 Hydroids proper in one order, on account of the identity of their structure and 

 of the similarity in the degree of complication of that structure, the types of this 

 order in Avhich the community consists of more Medusa-like Hydras, such as the 

 Pliysophoridaj and Diphyida?, must constitute a sub-order by themselves ; Physalia, 

 another sub-order, on account of the peculiarity of structure of the common Isase of 

 the community ; Velella and Porpita, another, for similar reasons ; and the true 



