182 SEA CUCUMBERS. 



movable tooth, which plays up and down. When the 

 cone is put together, the flat, dressed surfaces of the five 

 jaws, which stand round in a circle, are brought into 

 contact. All the food which is received at the mouth 

 must pass between these surfaces ; and as there are sys- 

 tems of muscles which enable them to play up and down 

 and across, a more perfect mill for grinding down the 

 food cannot well be conceived. We have not space more 

 fully to describe it, but the excellent popular account 

 given by Professor Jones,* and the examination of a 

 living specimen, will enable any one to understand the 

 uses of the several parts of this singular mechanism. 



Of the same class with the Sea Urchins and Star- 

 fishes, but exhibiting its characters in a weaker degree, 

 and showing in form and structure a tendency towards 

 the Annelides, are the Holothuriadce, or Sea Cucumbers, 

 of which several species occasionally come up in the 

 dredge. Their name, Sea Cucumbers, is very expres- 

 sive of their form in a contracted state, when the body 

 shrinks up into an oblong mass, slightly tapering to 

 each end, and rough with wrinkles and with the rows of 

 sucking-feet, which it has in common with the Urchins 

 and Star-fishes. In its texture it is tough and leathery, 

 without calcareous plates. The absence of a shell, the 

 presence of feathery tentacula about the mouth, and 

 the shape of the body, are differences between these 

 creatures and the Urchins ; while the two latter circum- 

 stances, together with the mode of progression by alter- 

 nate contractions and extensions of the body, connect 

 them with the Annelides. The general form of this 



" * General Outline of the Animal Kingdom," p. 16C, &.-. 



