ON THE LOCOMOTOR SYSTEM OE ECHINODERMATA. 
851 
and which may have strings and edges so fine as to admit of being enclosed by the 
forceps. Again, the instantaneous activity with which they all close round and seize 
a moving body of a size that admits of their seizing it, is suggestive of the objects 
which they are adapted to seize being objects which rapidly brush over the surface of 
the shell, and therefore objects which, if they are to be seized at all, must be seized 
instantaneously. Lastly, we find, on experimenting upon pedicellarise whether in situ 
or when separated from the Echinus, that the clasping action of the forceps is precisely 
adapted to the function 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 pedicellarise 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. That is to say, the pedicellarise tightly fix the object which 
they have caught for a time sufficient to enable the ambulacral suckers to establish 
their connexions 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.* 
On the whole, therefore, we can entertain but little doubt concerning the main 
function at least of the trident pedicellarise in the Echinus. But criticism will, of 
course, immediately object that in other Echinoderms these organs are too small or 
too few to be of any use in assisting locomotion in the way just described. The only 
answer to this objection is, that in ascertaining the function of any organ it is safest to 
study the activities of that organ in its most developed, or least degenerated, form. 
We could not, for instance, ever ascertain the function of the spines in any of the 
Echinodermata, if we were to consider these structures only in the Star-fishes and 
Holothurians, and if the pedicellarke seem to be so small in Star-fish as not to appear 
capable of performing the function here assigned to them in Echinus, the explanation 
probably is that, as in the analogous cases of the spines, changed habits of life on the 
part of the animals have caused these inherited appendages to dwindle from disuse. 
Thus, for instance, Brittle-stars never climb sea-weed-covered-rocks at all, and those 
Star-fish which do so have their ambulacral feet restricted to the ventral surface ; it 
would therefore be useless for these animals to have well-developed pedicellarise, 
adapted to hold sea-weeds steady in the manner which may be of so much use to the 
globular Echinus, who throws out on all sides feet feeling for attachments. Therefore, 
whether the pedicellarise of these other Echinoderms perform any function that yet 
remains to be detected, or whether they are mere rudiments now useless, we think 
* When pedicellarise are detached from the Echinus, however, it is frequently observable that their 
grasp becomes, as it were, spasmodic, and endures for an indefinite time. For instance, it is not unusual 
to see a pedicellaria, which has been torn from its root while clutching a pedicel, carried about holding 
on to the pedicel for a very long time. But this spasmodic or continuous grasp of the organ when severed 
we have not observed to occur when the organ is in situ. 
5 R 2 
