﻿April, 1857.] 



ELLIOTT SOCIETY. 



175 



inner membranes of the air-vessel. These sub-divisions in 

 Physalia and the tubular stem in Rhizophysa are in this view the 

 homologues of the free digestive trunk in Eudoxia, and in both 

 cases bear the specialized medusa-buds which in these communi- 

 ties perform the most essential functions of life. 



The Physalidae possess neither swim-bells nor bracts, and are by 

 this negative character separated from Physophidse. The sexual 

 medusae in Physalia, and apparently also in Rhyzophysa, are de- 

 veloped in grape-like bunches as in many Tubularidae. 



It is quite possible that Eschscholtz' genus, Discolabe, ought to 

 be included in this group. 



PHYSALIA. 



The genus Physalia is distinguished by an air-vessel having a 

 bilateral symmetry,* and surmounted by a crest divided inter- 

 nally by membranous partitions. The development of the bud- 

 ding diverticula from the digestive trunk, is so great, that the 

 latter loses its character of an elongated tube. In certain species 

 (P. utriculus Esch.) there are diverticula of uncertain nature on 

 the upper surface of the medusa-bearing extremity of the air-blad- 

 der or basal-medusa, which are wanting in Physalia. These may 

 constitute a distinct genus. The distinctions of the three princi- 

 pal groups of Lesson are perhaps due to difference in relative age. 



So much for the air-bladder which represents the basal disk 

 and upper portion of the digestive cavity in Eudoxia. The lower 

 or free portion of the latter is cartilaginous and divaricates more 

 and more as it grows older. From these divarications spring 

 digestive trunks, each with a tentaculiform individual near its 

 base, as in other genera. There are two (perhaps in some 

 species even more) sizes of these digestive trunks and tentacula. 

 The greater are the fewer in number. Besides these four classes 

 there are near the extremity of the branches bundles of digestive 

 trunks with no oral opening, containing peculiar brown cells 

 which Gluatrefages considers hepatic. The terminal divarica- 

 tions of the main branches support grape-like clusters of sexual 

 medusae. The outermost of the latter have the form of peduncu- 



* That extremity of the air-vessel in which is found the aperture of communi- 

 cation with the external air has been called the anterior, but it is evident that 

 such terms must be entirely arbitrary. If either extremity can receive such a 

 designation, it would in my view be the opposite, since it would be that which is 

 homologous with the anterior extremity of Holothuridse. 



