CHAPTER VL 

 SUB-CLASS SIPHONOPHORA. 



THE animals included under the name of Siphonophora 

 are often known as the " oceanic Hydrozoa," as they are not 

 fixed like the Hydroid zoophytes, but are found swimming at 

 the surface of the open ocean, far from land. They are all 

 singularly delicate and beautiful organisms, but they require 

 little notice here. They are distinguished from the Hydroid 

 zoophytes, which we have been just considering, by the fact 

 that the hydrosoma consists of numerous polypites, united by 

 a common trunk or ccenosarc, which is very rarely branched, 

 and is never furnished with any hard outer covering or poly- 

 pary, so that it remains permanently soft and flexible through- 

 out life. As in the Hydroida, the reproductive organs are in the 

 form of special buds, which have the power of developing the 

 essential elements of generation, and which are often detached 

 as free-swimming medusoids. 



The entire sub-class is divided into two great groups or 

 orders, and it will be sufficient to consider shortly a typical 

 form of each. In the first order that of the Calycophoridce 

 the ccenosarc is thread-like, cylindrical, unbranched, and highly 

 contractile. The cavity of the coenosarc dilates at one end 

 into a peculiar ciliated chamber, which is the distinguishing 

 character of the order. The name of Calycophoridce, (Gr. 

 kalux, a cup ; and phero, I bear) is, however, derived from 

 another circumstance namely, that one end of the coenosarc 

 is always furnished with a series of bell-shaped disks, which 

 are known as "swimming-bells" or " nectocalyces." Each 

 nectocalyx consists of a bell-shaped cup (Fig. 19, v, v'), at- 

 tached by its base to the ccenosarc, and having its cavity 

 turned outward. In the substance of the disk run at least 

 four canals, which communicate with the cavity of the coeno- 



