COMMON EGG-URCHIN. 159 



tenna?, partly to seize the small animals which serve for its 

 sustenance, partly to lay hold of whatever might approach 

 their sensitive skin which covers the surface of the shell, 

 and thus in conjunction with the prickles protect it from 

 injury.' 1 '' He says that some which he had cut off moved 

 six hours afterwards with considerable liveliness. 



The description of the structure of these bodies as given 

 by M. Sars is so accurate that I need not add to it ; suffice 

 to say, I have also observed the rows of globules, the ar- 

 rangement of the calcareous parts, &c. in all the kinds of 

 Pedicellaria he describes. Of one point I cannot satisfy 

 myself, that there is a knob on the shell for every Pedicel- 

 laria ; moreover, they are not all on the shell, there are 

 great numbers on the oral membrane. I have over and 

 over again repeated M. Sars^ experiment of irritating the 

 skin, without obtaining the result he mentions. In no 

 case did the Pedicellaria bend of themselves towards the 

 irritated point, and the same I may say of the spines. 

 No irritation of one Pedicellaria affected those in its 

 neighbourhood unless they were accidentally touched. 

 The fleshy substance of these bodies is exactly that of 

 many animals of acritous structure, and they are so 

 scattered over the body of the Urchin, without reference 

 to form or fig*ure, that it is almost impossible to assign 

 them, or the various kinds of them, special offices in the 

 animal's economy. Each seems independent of the others, 

 and of the Sea-Urchin, which is not the case with the 

 spines. As to their resemblance to an Echinus spine 

 I can see but little. I agree with M. Sars in believing 

 Schweigger to have been mistaken when he stated Pedi- 

 cellariae to exist on certain testaceous Mollusca ; but can 

 by no means consider the question of their nature to be 

 settled, and find myself quite undecided as to whether they 



