258 OCTOBER. 



breeze playing upon it, imparts to the whole animal, 

 according to Mr. Bennett, a rotatory motion. 1 



Both these oceanic forms of the class Hydrozoa agree 

 in being quite unprovided with any apparatus for loco- 

 motion. Though their parts can be moved among 

 themselves, and sometimes with much vigour, as we j 

 have seen in the case of the tentacles of the Pliysalia, 

 yet the whole organism would be absolutely confined 

 for life to one spot, were the elements motionless around 

 it : it is merely passively driven hither and thither by 

 the winds and waves. But there are other members of 

 the class, and even some belonging to the same order, 

 which have express organs of locomotion. A most ex- 

 quisite example is found in Stephanomia, of which a 

 specimen was taken in Kingstown harbour in July 1856, 

 by Mr. Joseph Greene, and described and figured in 

 the " Proceedings of the Dublin University Zoological 

 Association" for that year. The float (pneumatocysf) 

 is a small bladder, which is filled with air, and which 

 has the appearance, when alive, of a globule of quick- 

 silver ; while the slight inequalities of its surface reflect 

 the light in such a manner that it often looks as if a j 

 fine network of crimson veins ramified over its surface. 

 From the end of this oval bladder a long fleshy tube 



1 See his Gatherings in Australasia, for much interesting information on 

 both these animals. 



