180 THE AQUARIAN NATURALIST. 



that give to the Crinoidea such a beautiful appear- 

 ance ; at one time spreading outwards like the petals 

 of a flower, at another rolled inwards over the mouth 

 of the animal like an unexpanded bud. From their 

 structure and movements, it can hardly be doubted 

 that they serve to seize upon and convey to the mouth 

 whatever has been destined for its food, and which 

 probably consists of every minute animal its powers 

 enable it to overcome. 



The body, situated in the centre of the rays, pre- 

 sents a central opening or mouth, formed by five 

 petal-like valves, which possess the power of expand- 

 ing or of folding down closely, so as to shut up the 

 mouth; within these valves, when expanded, several 

 soft tentacula present themselves, similar in structure 

 to the tentacula of the arms. The most remarkable 

 part of its structure, however, consists in the existence 

 of a distinct termination to the alimentary canal, 

 which, perforating the side of the body, ends in a 

 tubular opening of considerable size, and capable of a 

 remarkable degree of elongation, being at times as 

 conspicuous in this respect as at others it is difficult 

 to discern. This unlooked-for peculiarity, quite dif- 

 ferent from what is met with in the generality of star- 

 fishes, subsequently led to the detection of a similar 

 arrangement in the genus Comatula, a discovery, the 

 importance of which the reader will immediately ap- 

 preciate. 



The smallest specimens of Pentacrinus observed by 

 Mr. Thompson did not exceed one eighth of an inch 

 in height. In this stage the animal resembles a little 

 club, fixed by an expanded basis, and giving exit at 



