STAR-FISH AND SEA-URCHINS. 287 
which we are considering ; for not only is the force 
exerted by the forceps during their contraction of 
an astonishing amount for the size of the organ 
(the serrated mandibles of the trident pedicellarize 
holding on with a tenacity that can only have 
reference to some objects liable to be dragged away 
from their grasp), but it is very suggestive that this 
wonderfully tenacious hold is spontaneously relaxed 
after a minute or two. This is to say, the pedi- 
cellariz tightly fix the object which they have 
caught for a time sufficient to enable the ambulacral 
suckers to establish their connections with it, and 
then they spontaneously leave go ; their grasp is not 
only so exceedingly powerful while it lasts, but it is 
as a rule timed to suit the requirements of the 
pedicels. * 
Concerning the physiology of the pedicellarize 
little further remains to be said. It may be stated, 
however, that the mandibles, which are constantly 
* A further proof that this is at least one of the functions of 
the pedicellariz is furnished by a simple experiment. If an 
Echinus is allowed to attach its feet toa glass plate held just 
above its ab-oral pole, and this plate be then raised in the water 
so that the Echinus is freely suspended in the water by means of 
its feet alone, the animal feels, as it were, that its anchorage 
is insecure, and actively moves about its unattached feet 
to seek for other solid surfaces. Under such circumstances 
it may be observed that the pedicellariz also become active, and 
especially so near the surface of attachment, as if seeking for 
pieces of sea-weed. If a piece is presented to them, they lay 
hold upon it with vigour. 
- Of course the pedicellariz may also have other functions to 
perform, and in a Star-fish Mr. Sladen has seen them engaged in 
cleaning the surface of the animal ; but we cannot doubt that at 
least in Echinus their main function is that which we have stated. 
