STAR-FISH AND SEA-Ur.CIIINS. 319 



spines, and pedicellarire together, so that they all 

 ai)proxiinate a point of irritation sifAiated anywhere 

 in that plexus ; (2) of an internal nervous plexus 

 which is everywlicre in communication through the 

 thickness of the shell with the external, and the 

 function of which is that of bringing the feet, spines, 

 and probably also the pedicellarise into relation 

 with the o'reat co-ordinatino^ nerve-centre situated 



O CD 



round the mouth ; (3) of central nervous matter 

 which is mainly gathered round the mouth, and 

 there presides exclusively over the co-ordinated 

 action of the spines, and in large part also over 

 the co-ordinated action of the feet, but which is 

 further in part distributed along the courses of the 

 main nerve-trunks, and so secures co-ordination of 

 ieet even in separated segments of the animal. 



Special Senses. 



Before concluding, I must say a few words on 

 the experiments whereby we sought to test for the 

 presence in Echinoderms of the special senses of 

 sight and smell. 



We have found unequivocal evidence of the Star- 

 fish (with the exception of the Brittle-stars) and 

 the Echini manifesting a strong disposition to crawl 

 tow^ards, and remain in, the light. Thus, if a large 

 tank be completely darkened, except at one end 

 where a narrow slit of light is admitted, and if a 

 number of Star-fish and Echini be scattered over 

 the floor of the tank, in a few hours the whole 

 number, with the exception of perhaps a few per 



