DIVISIONS OF THE HYDROZOA. a7 
The tentacles are usually of a very great length, and furnished 
with lateral branches, provided with numerous thread-cells. 
The reproductive organs of the Calycophorid@ are in the form 
of medusiform gonophores, which are budded from the stalks 
of the polypites, and which are mostly detached to lead an inde- 
pendent existence. 
The second order of the oceanic Hydrozoa is that of the 
Physophoride (Gr. physa, a bladder; and phero, I carry), of 
which the most familiar, though not the most typical, example 
is the Portuguese man-of-war, Physalia utriculus (fig. 24, a). 
The Physophoride are distinguished from the organisms which 
we have been just considering by the fact that the proximal 
extremity of the coenosarc is developed into a structure which is 
known as the “float” or “pneumatophore.” The float contains a 
larger or smaller sac, composed of some elastic horny substance, 
probably chitine, often communicating with the exterior by one 
or more apertures, and always more or less completely filled with 
air. This sac is enclosed in a reflection of the ectoderm and 
endoderm, so. that it is really outside the cavity of the coenosarc 
(fig. 23, a). The function of the float is no doubt that of en- 
abling the organism to maintain its position at the surface of 
the sea. As in the Calycophorida, the coenosarc is always per- 
fectly flexible, contractile, and soft, and is never furnished with 
any chitinous covering or polypary. There may or may not 
be swimming-bells or nectocalyces, and the tentacles are very 
complicated in structure, and often attain a length of many feet. 
The polypites present no special points of interest, but are often 
furnished with the protective plates, which have been already 
spoken of as “ bracts.” 
As a good example of the Physophoride, the Portuguese 
man-of-war may be taken (fig. 24, a). It is composed of a 
large spindle-shaped float, often of several inches in length, 
upon the under surface of which are arranged a number of 
polypites, together with highly-contractile tentacles of great 
length, and reproductive organs. The tentacles are richly 
furnished with thread-cells; and it has the power of stinging 
very severely. Physalia is commonly found floating at the 
surface of tropical and sub-tropical seas, and fleets of it are 
occasionally driven upon our own shores. 
Another very beautiful member of the Physophoride is the 
Velella vulgaris, which occurs abundantly in many seas, and is 
