400 THE HOMOLOGIES OF PEDICELLARLE. 
One may see the rejected bits of food passing rapidly along the 
m upon which these pedicellariz occur in greatest number, as 
if they were so many little roads fur the conveying away of the 
refuse matter; nor do the forks cease from their labor till the 
surface of the animal is completely clean and free from 
Fig. 82, any foreign substance. Were it not for the Fig-%. 
pedicellariz the food thus rejected would be- 
come entangled among the tentacles and spines, 
and remain stranded there till the motion of the 
the water washed it away. These curious little 
organs have other offices besides this very laud- 
able and useful one of scavenger. They occur 
over the whole body, while they pass the excre- 
ments only along certain given lines. They are 
especially numerous about the mouth where they 
are much shorter (Fig. 79) and more compact ; 
the muscular sheath below the head is quite 
short, the tripartite head resting directly upon the 
limestone rod of the 
On watching the movements of the pedicellariz we find that 
they are extremely active, opening and shutting their forks un- 
ceasingly, reaching forward in every possible direction, the flexi- 
bility 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 un- 
fortunate little crustacean, worm or mollusk 
which has become entangled among the spines. 
_, They do not seem to pass their prey to the mouth 
Is ` (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 
pedicellariz as forks. 
Among the different kinds of sea-urchins we find a great many 
- modifications of the pedicellarie just described. In the genus 
‘Cidaris the muscular sheath below the head is short and slender 
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of bundles of longitudinal rods. In some Spatangoids the 
(Fi ig. 82) ; ; it is placed upon the summit of a limestone rod made 
