560 STRUCTURE AND HABITS OF THE PHYSALIA. 



of the sea : a position perhaps rendered necessary when, from 

 drying winds, the top of the membrane has become rigid. — 

 Its most favourite position in the water is resumed by again 

 taking an elongated shape ; and it must be remembered that 

 these actions take place in an animal, in which minute re- 

 search has not been able to detect a nervous system. These 

 motions also, of a creature inflated with air, derive much in- 

 terest from the explanation they afford of those faculties of 

 some animals which appear to have received an erroneous or 

 imperfect interpretation. Thus the prehensile organs of Echi- 

 nus and Asterias, which are hollow, and capable of being 

 drawn close to or within the body, are described as being pro- 

 truded by simply propelling a fluid along their course, which 

 fluid, when no longer wanted for this purpose, is again re- 

 turned to the cavity. At this point the explanation ends ; 

 propulsion being regarded as the sole object of the function. 

 Such, however, does not appear to be the case ; the disten- 

 sion effected by the propulsion of fluid in the radiate animals, 

 and of air in Physalia, being only the first step in the pro- 

 cess, and providing a fulcrum for the support of muscular ef- 

 fort the chief object in view. In the tube of the Lepades the 

 action is of a similar kind, though more complicated, owing 

 perhaps to its annulated structure. The distension caused by 

 the contained fluid in the latter is less considerable, and the 

 animal sometimes hangs in a flaccid state, at its full length. 

 When about to move, compression of the fluid fixes the cen- 

 tre of motion, which is rendered still more energetic by col- 

 lecting and fixing it at the root, or in particular departments. 



The remarks here offered may be extended to many of the 

 voluntary motions of other animals of soft texture ; develop- 

 ing a contrivance by which apparent contrarieties are recon- 

 ciled, and creatures having so little firmness in their com- 

 position enabled to perform motions requiring tense support : 

 the fulcrum which in the higher animals is the heaviest por- 

 tion of their structure, and acts by gravity as well as strength, 

 being in them no less effective as a moving power, and yet so 

 light as to serve the office of a balloon. 



It is well known that the Physalia, and several species of 

 Medusa, are capable of inflicting a stinging sensation on the 

 hands that touch them. The certainty of this admits of no 

 doubt; the effect being severe even in persons whose skin 

 cannot be supposed endued with remarkable delicacy. A 

 sailor-boy, a short time since, was so severely affected from 

 handling a single specimen, that the skin peeled from the 

 whole surface of his hand. Yet, with the intention of expe- 



