72 INVERTEBRATE ANIMALS. 



CHArTETl A'll. 



SUB-CLASS SIPHONOPHOEA. 



The aiiiin:ils included under the name of Siphonopliora five nften 

 known as the " Uceanic Hydrozoa," as they are not fixed hke the 

 Hydroid Zoophytes, but ai'e found swimuiiug at the suiface of the 

 open ocean, far froni lanil. They are all singularly delicate and 

 beautifid organisms, but they require little notice here. They are 

 distinguished from the Hydroid Zoophytes, wliich we have been just 

 considering, by the fact tliat the hy<lrosonia consists of numerous 

 polypites, united by a connuon trunk or co?nosarc, which is very 

 I'arely branchwl, and is never furnished with any hard outer cover- 

 ing (jr polypary, s(j that it remains permanently soft and flexible 

 throughout life. The proximal end of the coenosarc, as already re- 

 markeil, is not fixed, or capable of being fixed, to any solid object, 

 but is variously modified to suit the requirements of the floating 

 ci.ilony. As in tlie llijih-niiln, the reproductive organs are in the 

 foi'm of special buds, which have the power of developing the essen- 

 tial elements of generation, and wliich are often detached as free- 

 swinnning niedusoids. 



The entire sub-class is divideil into two great groups or orders, 

 anil it will be suflicient to consider shoi'tly a typical form of each. 

 In the first oriler — that of the Cali/foplioriilte—^he creuosarc is thread- 

 like, cylindrii-al, unbrauched, .-ind highly contractile. The cavity of 

 the CNiiosarc dilates proximally into a peculiar ciliated chandler, 

 which is the distinguishing character of the order. The name tif 

 Vdhicitphoi-iihe ((ir. knj-ii.i\ a cup; and phero, I bear), is, however, 

 derived from another circumstance — namely, that the pioximal end 

 of the ctenosarc is ahv.iys furnished with a series of bell-shajied discs, 

 which ai'e known as "swimming-bells" or " nectocalyces." Each 

 nectoc;ilyx consists of .a bell-shiqied cup (fig. 39, ;/'), attached by its 

 b;ise to the C(euos,-irc, and ha\ing its cavity turned outwards. In 

 the snbst.'ince of the <lise riui at least four canals, which connunni- 

 r;itc with the cavity of the cn'uiisarc, and |>riiceed to the margin of 

 the licll, whci'e they all ojicu into a circular vessel. The mouth of 



