104 LOWER INVERTEBRATES. 



minute tasters which wave about in the water with great freoidom. The polyp- 

 stem also, instead of being covered throughout its whole length with covering- 



FiQ. 96. — Portion of Apolemia, 



scales, has these structures arranged at intervals and in clusters, each with tasters, 

 polypites, and sexual bodies. 



Ordek II. — PNEUMATOPHORiE. 



There are two genera of Siphonophora closely related to each other and to the 

 group of Physophorte already studied, which are now looked upon as forming a group 

 by themselves.' These genera include the w'ell-known Portuguese Man-of-War or 

 Physalia, often ei-roneously called by sailors the Nautilus, and a less common genus, 

 Ithizophysa, one of the most bizarre forms of these animals. 



Physalia is one of the most common of all the Siphonophora in tropical oceans. 

 The most conspicuous part of this animal, as it floats along on the surface of the water, 

 is an enlarged air-bladder, six or eight inches in length. On the upper side of this 

 float there is a raised crest colored by brilliant blues, yellows, and pinks. On the 

 under side of the same there hang a great variety of appendages of several kinds. 

 There are feeding-mouths or polypites, flask-shaped bodies resembling tasters with 

 long tentacles, which, as the animal floats in the water, extend far behind it in the 

 water as magnificent streamers, and grape-like clusters of sexual bodies. The Physalia 

 is wholly destitute of a tube-like axis, and as it floats on the surface of the water, 

 resembles more a bladder with richly variegated walls, than the tube-like forms which 

 we have already considered. 



The closest relative to Physalia, as far as anatomy goes, to which affinity also what 

 is known of their development adds additional evidence, is the strange genus Rhizo- 

 physa. JRMzophysa is a simple skeleton of a siphonophore. It is the axis of an 



