198 



HOLOTHURIADvR. 



these suckers, the Holothuriadce move as Annelides, by the 

 extension and contraction of their bodies. They have a 

 mouth and an anus, each terminal, and placed at opposite 

 extremities of their bodies. The mouth is surrounded by 

 plumose tentacula, the number of which, when they are 

 complete, is always a multiple of five ; but as these ani- 

 mals are singularly subject to the loss or absence of parts, 

 in individuals of the various species much confusion has 

 arisen from the establishment of supposititious species 

 from characters founded on abnormal numbers of the 

 parts. The tentacula are ramose cirrhi ; they can be 

 retracted within the mouth, and sometimes when in cap- 

 tivity the animal will not exsert them for 

 days tog-ether, though otherwise active. 

 They are drawn in with the skin, and 

 when we cut open a Holothuria having 

 its tentacula retracted, we find them in 

 the centre of the dental circle. The cir- 

 cle of teeth is analogous to that of the 

 Echini. The oesophagus passes through it, and opens into 

 a more or less muscular stomach, from which an intestine, 

 often very complicated, proceeds to the posterior extremity 

 of the body, where it opens into a funnel-shaped cloacum, 

 into which also open the two tree-like respiratory organs. 

 There is a vascular circle (and some say a nervous cord,) 

 surrounding the mouth, and vessels are distributed from it 

 to various parts of the body and organs. One or more 

 sacs of a pyriform shape depend from a vessel surrounding 

 the pharynx, and are by many believed to be salivary 

 organs. Mr. Goodsir has found a sac containing cal- 

 careous concretions on one side of the mouth in certain 

 species. This he regards as a madreporiform tubercle or 

 nucleus. The ovaries are in many species very numerous. 



