56 



OPHIUR.E. 



the shores of the Isle of Man. On the Irish shores Mr. 

 Thompson and Mr. Hyndman take it by dredging in the 

 lochs of Strangford and Belfast, and Mr. Ball in Dublin 

 Bay. 



In texture this Ophiocoma is much more leathery than 

 its allies. It is a good subject in which to examine the 

 nervous system. Surrounding the mouth, but at some 

 distance from it, is a white nervous cord, which seems 

 double ; radiating from it are fifteen pairs of nervous 

 threads, which are arranged in threes, but have not a 

 common origin, — indeed, there appear to be no ganglionic 

 enlargements. Of each set of three pairs the central goes 

 to the body between the rays, and the two lateral run 

 up the sides of two different rays, so that each ray is pro- 

 vided with two pairs from two different sets. This ar- 

 rangement is very distinct and easily seen, by removing the 

 upper surface of the disk and the enclosed stomach and 

 ovaries. 



