BEROE. 195 



extend down its sides, like those of a melon ; 

 and along each of these is attached a set of little 

 membranes, extended horizontally, and snp- 

 ported on radiating fibres ; so that they bear a 

 pretty exact resemblance to the fin of a fish. 

 Their action is not nnlike that of the wings of a 

 bird ; for they are made to flap up and down, 

 striking the water vertically, and communicating 

 an ascending impulse to the body. This animal 

 is also provided w ith two very long and slender 

 processes, which come out from the sides of the 

 body, and from these a great number of still 

 finer filaments, or cilia, proceed : the whole 

 apparatus is highly sensitive and irritable, and 

 on the slightest touch the filaments are thrown 

 into spiral coils, and retract rapidly within the 

 body. They thus act the part of tentacula, or 

 delicate organs both of touch and of prehen- 

 sion.* It was observed by Fabricius, that when 

 a Beroe is cut into many pieces, each piece con- 

 tinues to live, and to swim about by the action 

 of the cilia, which still continue their vibratory 

 motions. 



In two other genera of Acalepha, the Porpita 

 and the Velella^ provision is made for the me- 

 chanical support of the soft gelatinous mass, by 

 means of an internal cartilage. In the former, 

 this cartilage is of a circular form ; in the latter, 



* See a description of the Beroe jnleus. Lam. by Dr. Grant, in 

 the Transactions of the Zoological Society of London, vol. i. p. 9. 



