390 ECHINODERMATA, 



CLASS I. 



ECHINODERMATA *. 



The Echinodermata are the most complicated animals of this divi- 

 sion. Invested witli a well organized skin, frequently supported by 

 a sort of skeleton, and armed with points, or movable and articulated 

 spines, they have an internal cavity in which distinct and floating 

 viscera may be perceived. A sort of vascular system, which it is 

 true does not extend throughout the body, keeps up a communica- 

 tion with various parts of the intestine, and with the organs of respi- 

 ration, which are generally distinct. Threads are also seen in seve- 

 ral, which may act as nerves, but which are never arranged with the 

 regularity and fixed order of those in the animals of the two preced- 

 ing divisions of the Invertebrata. 



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 want- 

 ing. 



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 cylindrical and 

 membranous tentacula, each one terminated by a little disk which 

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

 mains 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 extremities, that 

 these animals effect their progressive motions. Vessels proceeding 

 from these feet extend to trunks which correspond to their ranges, 



* The Rad.iircs Echiiiodcimes of M. de Lam.arck. 



