R62 PEDICELLARLE. 



are arranged concentrically instead of on one plane, ami when closed they 

 fit into one another as neatly as the pieces of a puzzle. PI. X. f. 15 ; PI. 

 XI'. f. u represent end views of some of these pedicellariae. 



If we watch a sea-urchin after he has been feeding, we shall learn at least 

 one of the offices which this singular organ perforins in the general economy 

 of the animal. That part of the food which he ejects passes <>ut of the anus, 

 an opening on the summit of the body in the small area where the zones of 

 which the shell is composed converge. The rejected particles, thrown out in 

 the shape of pellets, are received on these little folks, which close upon them 

 like forceps, and they are passed from one to the other, down the side of 

 the body, till they are dropped oil' into the water. Nothing is more curious 

 ami entertaining than to watch the neatness and accuracy with which this 

 process is performed. One may see the rejected bits of food passing rapidly 

 along the lines upon which these pedicellariae occur in greatest numbers, as 

 if they were so many little roads for the conveying away of the refuse mat- 

 ter ; nor do the forks cease from their labor till the surface of the animal is 

 completely clean and free from an}' foreign substance. Were it not for the 

 pedicellaria' the food thus rejected would become entangled among the ten- 

 tacles and spines, and remain stranded there till the motion of the water 

 washed it away. These curious little organs have other offices besides this 

 very laudable and useful one of scavenger. They occur over the whole 

 body, while they pass the excrements only along certain given lines. They 

 are specially numerous about the mouth, where they are much shorter (PL 

 X.f. 9, m) and more compact ; the muscular sheath below the head is quite 

 short, the tripartite head resting directly upon the limestone rod of the base. 



On watching the movements of the pedicellaria' we find that they are 

 extremely active, opening and shutting their forks unceasingly, reaching 

 forward in every possible direction, the flexibility of the sheath enabling 

 them to sweep in all the corners and recesses between the spines, and occa- 

 sionally they are rewarded by catching hold of some unfortunate little crus- 

 tacean, worm, or mollusk which has become entangled among the spines. 

 They do not seem to pass their prey to the mouth (at least I have never 

 succeeded in seeing sea-urchins pass the food thus caught), but merely 

 throw it off from the surface like any other refuse matter. Their mode of 

 eating, also, — a sort of browsing, by means of their sharp teeth along the 

 surface of the rocks, — does not favor the idea of using the pedicellaria' as 

 forks. 



