74 



INVERTEBRATE ANIMALS. 



of the Calycophoridm are in the form of medusiforra gonophores, 

 which are budded from the stalkg of the polypites, and which are 

 mostly detached to lead an independent existence. 



The second order of the Oceanic Hydrozoa is that of the Pkyso- 

 phoridoe (Gr. physa, a bladder ; and phero, I carry), of which the 

 most familiar, though not the most typical, example is the Portu- 

 guese Man-of-war, Physalia (fig. 40, a). The Fhysopkoridm are 

 distinguished from the organisms which we have been just consider- 

 ing by the fact that the proximal extremity of the coenosarc is devel- 



. 40. — a Portuguese Man-of-war (Physalia). 

 b Vclella vulgaris. 



oped into a structure which is known as the " float " or " pneumato- 

 phore." The float contains a larger or smaller sac, composed of 

 some elastic horny substance, probably chitiiie, often communicating 

 with the exterior by one or more apertures, and always more or less 

 completely filled with air. The function of the float is ]io doubt 

 that of enabling the organism to maintain its position at the surface 

 of the sea. As in the Galycophoridce, the ccenosarc is always perfectly 

 flexible, contractile, and soft, and is never furnished with any 



