197 



holothuriam:, 



OR CIRRHO-VERMIGRADE ECHINODERMATA. 



A Holothuria may be regarded in one light as a soft 

 Sea-Urchin, in another as a radiated animal, approximating 

 the Annelid.es. The radiation of the surface is more or 

 less complete in all the genera of Holothuriadse : the in- 

 ternal organisation is mostly bilateral. The skin is usually 

 soft and leathery ; in a few genera strengthened by cal- 

 careous or horny spines. Five avenues of suckers separate 

 the body into as many longitudinal segments, which in the 

 majority are of equal, or nearly equal dimensions. In some 

 the suckers are developed only on one side, so that the 

 animal, when creeping, presents in a manner a back and a 

 belly. The suckers are similar to those of the true Star- 

 fishes and Sea-Urchins. Besides progression by means of 



