880 
MR. G. J. ROMANES AND PROFESSOR J. C. EWART 
of the spines, without assistance from any of the pedicellarise. Being of a nearly 
spherical shape and somewhat firm consistence, their tendency is to roll down the 
sides of the globular animal, and to facilitate this movement the spines in their course 
diverge as soon as contact takes place—the pellet being thus allowed to pass between 
the spines with very little delay, and when brought up by other spines or stalks of 
pedicellarise lower down in the series, these similarly diverge, and so on, till the pellet 
arrives at the equator of the animal, when it drops perpendicularly off the shell. We 
have watched the process over and over again, and have been so struck with the 
methodical action of the spines concerned in it that we find it impossible to entertain 
any doubt on the question whether they are alone sufficient to perform the process, or 
require any considerable assistance from the pedicellarise. The assistance which the 
latter organs furnish in this process is only occasional, and seldom seems to be urgently 
required; it appears to us clearly but an accessory, if not an accidental function, for 
the performance of which the development of these organs cannot have been neces¬ 
sitated. And, direct observation apart, this view would seem to be rendered suffi¬ 
ciently obvious by the fact that these pedicellarise are not restricted to the upper 
hemisphere of the animal, but occur also below the equatorial line, where they can 
never have a chance of seizing a dung-pellet at all. 
Direct observation again apart, the homologies of the pedicellarise would alone sug¬ 
gest that their function is probably subservient to locomotion. The valuable paper of 
Professor Agassiz already quoted derives its value from the clear demonstration which 
it supplies that the pedicellarise are modified spines, and therefore the most obvious 
view would seem to be that they have been modified for the purpose of acquiring 
special proficiency as grasping organs of locomotion, over and above that which is 
presented by the unmodified or stilt-like spine. 
On the whole, then, we believe that at least the pedicellarice tridentes are not only 
homologous with, but analogous to, the spines ; and therefore we demur to the state¬ 
ment of Professor Agassiz when he says, “ the same reasoning will readily suggest to 
the student of Echinoderms the homology of the so-called claws of Ophiurians and of 
the anchors of Holothurians which, although used for such totally different functions, 
being a sort of prehensile organ for locomotion along the ground, are in reality only 
in their turn modified spines, or different forms of pedicellarise.” There can be no 
question about the homology, and our observations have satisfied us that there can be 
as little question about the analogy. The opinion, therefore, which we have here 
italicised and which refers to the pedicellarise of Echinus, we think requires amendment; 
for observation has shown us that these organs here perform the same kind of func¬ 
tions as those which Professor Agassiz recognises the homologous organs to perform 
in Ophiurians and Holothurians, where—as he says, in words which follow the above 
quotation—“ the pedicellarise hooks and anchors perform the part of organs of 
prehension and locomotion at the same time.” 
Thus far we have been considering the case of the pedicellarice tridentes. The other 
