MR. G. J. ROMANES AND PROFESSOR J. C. EWART 
878 
selves composed of two distinct layers—an external and an internal, each of which 
presents a uniform structure of cells and fibres. 
In a division of his paper devoted to an account of physiological experiments, 
Fredericq records several observations which are identical with some of those 
recorded in the corresponding division of the present paper. Thus, he tried the effect 
of severing the five ambulacral trunks, and found, as we found, that, while the opera¬ 
tion did not entail paralysis of the pedicels, it did entail complete destruction of co¬ 
ordination between their five rows. He also observed the rioFting' movements of 
inverted Echini, and experimented on the effect upon these movements of severing 
the nerve-ring. Here, however, his results are not quite in accordance with ours, for 
he says that in no case does an Echinus when so mutilated succeed in righting itself; 
whereas we found, as before stated, that out of twelve perfectly fresh specimens so 
mutilated three were able to right themselves. We are quite sure that our results in 
this connexion are trustworthy; for, as these results were contrary to our expecta¬ 
tions, we took the precaution of altogether removing the lanterns from a number of 
perfectly fresh specimens, and found, as previously, that a proportion of one in four 
continued able to right themselves. 
Lastly, Fredericq observed the local reflex action of the spines and pedicellariae, 
and also the insulating effect upon this action of a closed line of section. He inferred 
from these observations the presence of an external plexus, but was unable to detect 
its presence histologically. 
We may now conclude this account of previous literature with a discussion of 
previous theories as to the function of the pedicellariae. 
In stating our opinion as to what we consider their main function, it seems desirable 
briefly to consider the functions which have been ascribed to these organs by previous 
observers. Professor Owen supposes, or supposed (‘ Comp. Anat. of Inverts/ p. 20o), 
that their work in the economy of the animal is that of removing parasitic growths 
from the shell; and somewhat allied to this view is that of Professor A. Agassiz, who 
regards the function of these appendages to be that of “ scavengers.” He says : “ If 
we w r atch a Sea Urchin after he has been feeding, we shall learn at least one of the 
offices which this singular organ performs in the general economy of the animal. That 
part of the food which he ejects passes out of the anus—an opening on the summit of 
the body in tire small area where the zones of which the shell is composed converge. 
The rejected particles, thrown out in the shape of pellets, are received on their little 
feeler-like forceps, and they are passed from one to the other down the side of the 
body till they are dropped oft’ into the water. Nothing is more curious and entertaming 
than to watch the neatness and accuracy with which this process is performed. One 
may see the rejected bits of food passing rapidly along the fines upon which the 
pedicellariae occur in greatest numbers, as if they were so many little roads for the 
carrying away of the refuse matter. Nor do the forks cease from their labour till the 
surface of the animal is completely clean and free from any foreign substance. Were 
