DIVISIONS OF THE HYDROZOA. 75 
CHAPTER VI. 
SUB-CLASS SIPHONOPHORA. 
THE animals included under the name of Szphonophora 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 0 * 
numerous polypites, united by a common trunk or ccenosarc, 
which is very rarely branched, and is never furnished ,with 
any hard outer covering or polypary, so that it remains perma- 
nently soft and flexible throughout life. The proximal end of 
the ccenosarc, as already remarked, is not fixed, or capable of 
being fixed, to any solid object, but is variously modified to suit 
the requirements of the floating colony. As in the Hydrozda, 
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 Calycophoride— 
the coenosarc is thread-like, cylindrical, unbranched, and highly 
contractile. The cavity of the coenosarc dilates proximally 
into a peculiar ciliated chamber, which is the distinguishing 
character of the order (fig. 23,3 0). The name of Calycophoride 
(Gr. kalux, a cup; and phero, I bear), is, however, derived from 
another circumstance—namely, that the proximal end of the 
ccenosarc is always furnished with a series of bell-shaped discs, 
which are known as “swimming-bells” or ‘“nectocalyces.” 
Each nectocalyx consists of a bell-shaped cup (fig. 23, 2), at- 
tached by its base to the coenosarc, and having its cavity turned 
é 
