164 



ECHINODEEMATA. 



Comatula. 



and capable of independent motion. The complicated arms of the 

 Comatula, therefore, are not, like those of the Polyp, merely adapted to 

 seize prey, but, from their superior firmness, may be used as so many 

 legs, enabling the animal to travel fron place to place. 



Setting out from 



this point to trace Fig. 81. 



the gradual develop- 

 ment of organization 

 in the Echinodermata, 

 we shall observe a pro- 

 gressive concentration 

 of their entire structure. 

 The central part, or vis- 

 ceral cavity, so small 

 in the Comatula when 

 compared to the com- 

 plicated rays derived 

 from it, enlarges in its 

 proportional dimensions 

 as the viscera con- 

 tained within it become 

 more perfect in their 

 arrangement, whilst, on 

 the other hand, the radiating or polyp form, so visible in Encrinus and 

 Comatula, becomes obliterated by degrees, until, at length, almost all 

 vestiges of it are lost, 

 or but obscurely recog- 

 nizable. 



In the Gorgonoce- 

 phalus (fig. 82), the pro- 

 portionate size of the 

 rays, when compared 

 with that of the central 

 disk, still preponde- 

 rates very considerably, 

 although even here 

 some concentration is 

 manifest. The second- 

 ary articulated fila- 

 ments appended to the 

 rays of Comatula are 

 no longer recognizable, 

 their place being sup- Gorgonocephaius. 



plied by the continual division and subdivision of the rays themselves : 

 the same end, however, is obtained in both cases ; for the numerous 



Fig. 82. 



