1884.] On the Nervous System of the Crinoidea. 75 



they differ much more widely both from Asterida and Ophiurida, than 

 those Orders differ from each other ; and while all recent researches 

 tend to show that Crinoidea are closely allied to Blastoidea and pro- 

 bably to Cystidea, they bring into view their points of difference from 

 all Echinoderms the aspect of whose mouths is downward, a distinc- 

 tion long since put forward by Leuckart as one of fundamental value. 



It was pointed out nearly twenty years ago by Sir Wy ville Thomson 

 and myself, that the canalisation or non-canalisation of the calcareous 

 segments of the Crinoidal skeleton, for the passage of the axial cords, 

 affords a distinctive character by which its proper radial portion can 

 be differentiated from the accessory pieces by which its arrangement 

 is often complicated and obscured. And the practical value of this 

 character has been recognised by various students of the extinct 

 types of the group, with this modification, that among the 

 Paleocrinoids the axial cords often lie in grooves which have not 

 closed-in to form canals, just as I have shown to be the case in 

 Antedon at a certain stage of the development of the radials. It is 

 obvious that the morphological value of this character becomes much 

 greater, if the axial cords are nerve-trunks which call into action the 

 complicated muscular apparatus of the arms, than if they are to be 

 regarded (with Ludwig) as merely unconsolidated portions of the 

 general basis-substance of the calcareous skeleton. 



Another point of interest Physiological rather than Morphological 

 is the existence of a definite nervous system, possessed of great 

 functional activity, which yet shows very little histological differenti- 

 ation. It can scarcely be doubted, I think, that there is here no defi- 

 nite distinction between ganglionic centres and nerve-trunks ; almost 

 every part of the apparatus being probably capable of originating 

 as well as of conducting. The peripheral branches distributed to the 

 perisome will, of course, be those by which sensory impressions will 

 be received ; while the branches distributed to the muscles will be 

 those which call forth their motor activity. But that the axial 

 cords of the arms are not mere conductors, seems proved by the per- 

 formance of active spontaneous movements by arms which have been 

 for several days detached from the body. And the connexion of 

 these cords with each other in the annular commissure and in the 

 quinquelocular centre, would seem to have reference rather to the 

 co-ordination of actions which would be otherwise independent, than 

 to a derivation of nerve-power from either of those sources. 



I cannot but think that I have now given sufficient reason why the 

 question I have raised should be no longer ignored, but should be 

 reconsidered in the light of the new facts and arguments I have 

 adduced in support of my views. Those who refuse to accept them, 

 are bound, I think, either to disprove the facts, or to show that 



