ON THE LOCOMOTOR SYSTEM OF ECHINODERMATA. 
879 
it not for the pediceUarise the faeces thus rejected would be entangled among the 
tentacles 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 scavengers : they occur over the whole body, while they pass the 
excrements only along certain given lines. They are especially numerous about the 
mouth, where they are much shorter and more compact. The muscular sheath below 
the head is quite short, the tripartite head resting directly upon the lines of the base. 
On watching the movements of the pediceUarise we find that they are extremely 
active, opening and shutting their forks unceasingly, reaching forward in every pos¬ 
sible direction, the flexibility of the sheath enabling them to sweep in all the corners 
and recesses between the spines; and occasionally they are rewarded by catching hold 
of some unfortunate little crustacean, worm, or mollusca 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 
threw 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 favour the idea of using the pediceUarise as feelers.”* 
From this account we gather that Professor Agassiz regards the main function of 
the pediceUarise to be that of removing excrement, although they may also act the 
part of general cleansers to remove any other undesirable substance—whether para¬ 
sitic or otherwise—from the general surface. This view has recently been confirmed 
by Mr. W. 0. Sladen, who says, in the course of an interesting paper,! “ Mr. Alex¬ 
ander Agassiz was, I believe, the first, who by actual observation assigned the true 
function to any of these organs. Unfortunately, Mr. Agassiz leaves the matter with¬ 
out saying which of the forms of this appendage was the agent employed. I also have 
seen the same operation performed ; and it was always the pedicellarice tridentes that 
came into use for the purpose; indeed, the most superficial examination would suggest 
that these alone could be employed for such a service, neither the pedicellarice globi- 
formes nor the pedicellarice triphyllce having valves capable of grasping so large a body 
as the ejected pellets in question. On the other hand, the jaws of the pedicellarice 
tridentes are admirably fitted for the purpose ; and that this is the chief use of that 
form of pediceUarise there seems but little doubt. 5 ’ 
Now r , restricting our consideration in the first instance to this form of pedicellaria, it 
seems d priori improbable that so elaborate and peculiar a structure should have been 
developed for the purpose supposed. To sustain the supposition, it would at least 
require to be shown that the excrement of Echinus is so difficult of removal that were 
it not for the action of these pediceUarise it would remain on the ab-oral pole of the 
animal in an amount, or for a time, that might be injurious. Yet we can confidently 
say that such is not the case. The dung-pellets are generally removed by the action 
* ‘ American Naturalist,’ vol. xii., pp. 399-400, 1873. 
t ‘Annals and Magazine of Nat. Hist.,' Aug., 1880, p. 101, et sea. 
