198 FUNCTIONS AND INSTINCTS. 



they were thus gifted, as their specific gravity 

 exceeds that of the water, they could not raise 

 themselves to the surface, where they are seen 

 swimming very gracefully ; as it were, by an 

 alternate systole and diastole, admitting and re- 

 jecting the sea-water. Several of them, 1 for it is 

 not common to them all, when touched, cause a 

 sensation similar to that produced by the sting of 

 a nettle : 2 it is supposed by some that this is done 

 by their tentacles, which are conjectured to have 

 little suckers, as indeed is very probable, which 

 adhere to the skin. This faculty, which is sup- 

 posed to be the lowest degree of the electric power 

 peculiar to several fishes, is found in other genera 

 of this tribe ; for instance, the Jamaica sea-nettle, 3 

 is said to affect the hands, when touched, still 

 more severely. Probably this faculty was given 

 to them by Providence, either for the defence of 

 their frail forms against their assailants, or to 

 enable them to secure their prey, this being the 

 general use of their numerous tentacles and 

 other organs. Lamarck observes, that some of 

 these animals are so large as to be more than a 

 foot in diameter, and that some weigh as much 

 as sixty pounds. Their multitudes are prodi- 

 gious, and, as well as the beroe, they are said to 

 form part of the food of the whale : they are 

 even devoured by some of their own class. The 



1 Rhizostoma* Cuv. Cephece Rhizostomce, Lam. 



2 See Appendix, note 22. 



3 Physalis pelagica. 



