500 ECHINODERMATA. 



We divide the Echinodermata into two orders: those furnished 

 with feet or at least with vesicular organs, so called on account of 

 their fulfilling similar functions; and those in which they are wanting. 



ORDER I. 

 PEDICELLATA. 



The Pedicellata are distinguished by organs of motion exclusively 

 peculiar to them. Their skin is pierced with a number of little 

 holes, arranged in very regular series, through which pass cylindri- 

 cal and membranous tentacula, each one terminated by a little disk 

 which acts like a cupping-glass. That portion of these tentacula 

 which remains within the body is vesicular; a humour is effused 

 through their entire cavity, and is either propelled at the will of the 

 animal into the exterior and cylindrical portion, which it distends, 

 or returns to the interior vesicle, when the former sinks and becomes 

 relaxed. It is by thus elongating and shortening their hundreds of 

 little feet or tentacula, and by fixing them by their cup-like extremi- 

 ties, that these animals effect their progressive motion. Vessels 

 proceeding from these feet extend to trunks which correspond to 

 their ranges, and which terminate near the mouth. They form a 

 system distinct from that of the intestinal vessels observed in some 

 species. 



LinnaBUS divided them into three very natural, but numerous ge- 

 nera, and composed of such various species, that they may be consi- 

 dered as forming three families. The 



ASTERIAS, Lin. 



Or Starfish, have been so called because their body is divided into rays 

 (generally five), in the centre of which, and underneath, is the mouth. 



The framework of their body is composed of small osseous pieces, vari- 

 ously combined, the arrangement of which merits examination. Their 

 power of reproduction is very great, as they not only reproduce the rays 

 which have been separately removed, but a single one with the central ray 

 remaining will reproduce all the others; for this reason their figure is fre- 

 quently irregular. 



ECHINUS, Lin. 

 The Edam, or Sea-Urchins, as they are termed, have the body invested by 



