212 RAMBLES OP A NATURALIST. 



incessantly vibrating and striking the surrounding 

 liquid, through which, notwithstanding their minute 

 size, they enable the creature to move with tolerable 

 rapidity, by means of the infinite number of their 

 impulsions, although these animals are often of com- 

 paratively large dimensions. 



Yet notwithstanding this great diversity in their 

 external forms, the Beroidae present a remarkable 

 uniformity of organisation. The internal cavities 

 are more or less elongated, the circulatory canals 

 are more or less ramified, but we everywhere dis- 

 cover the same organic arrangements. Whether 

 they resemble the Cestus or the Cydippe, all these 

 genera, although differing so widely in appearance, 

 seem to have been cast in the same mould, if we 

 merely have regard to their anatomical characters, 

 which, moreover, are very remarkable. Con- 

 sidered in relation to these, the Bero'idae approxi- 

 mate to the Medusae, and diverge most completely 

 from the Acephalous Molluscs, among which certain 

 modern authors have attempted to place them 

 next in order to the oyster and other kindred 

 bivalves.* We need only advance the following 

 fact in support of our statements. In the Ace- 

 phalous Molluscs the alimentary tube presents two 

 openings, one of which serves for the admission of 

 the food, and the other for the ejection of the in- 

 digestible residue; whilst in the Beroida?, as in all the 



* Amongst others De Blainville held this opinion ; but we are 

 probably doing him no injustice in inferring that he was chiefly led 

 to this view from the desire to differ from Cuvier. This naturalist, 

 however, also placed all the Siphonophora among the Mollusca. 



