1881.] Oil the Locomotor System of Ecliinodermata. 



11 



animal containing only a single row of pedicels is in many cases able 

 to perform this manoeuvre, we conclude, as already stated, that the 

 action of the pedicels is partly of a serial character, though largely 

 assisted by the co-ordinating influence that emanates from the nerve- 

 centre. 



The effect of this operation upon the spines and pedicellariae still 

 remains to be considered. No effect at all is produced upon the pedi- 

 cellaria? ; but upon the spines a profound influence is seen to be exercised. 

 Their spontaneity, indeed, remains unimpaired, as does also the func- 

 tion which they share with the pedicellariae of closing round any 

 instrument of stimulation ; likewise their power of responsive bristling 

 all over the animal when any part of the animal is severely stimulated 

 continues to be manifested as before, although for an hour or two after 

 the operation this power is suspended by shock. But the general co- 

 ordination of the spines is totally and permanently destroyed, for if 

 the animal be placed upon a table and a spirit-lamp flame held against 

 one side, although all the spines will manifest their bristling movements 

 (if the period of shock has been allowed to pass away), they will no 

 longer co-operate to remove the animal from the source of irritation. 

 These facts prove, 1st, that the general co-ordination of the spines is 

 wholly dependent upon the nerve-centre ; 2nd, that the spontaneity 

 and local reflex irritability are wholly independent of that centre — 

 they depend entirely upon the external nerve plexus ; and, 3rd, that 

 the universal nervous connexions revealed in the bristling movements 

 of the spines, and which, as shown by previously narrated experiments, 

 depend upon the hypothetical internal nerve plexus, are themselves in 

 nervous connexion with the nerve-centre. For only thus can we 

 explain the long period of shock which removal of this centre entails 

 upon the functions of this supposed internal plexus. Nevertheless, 

 the fact that these functions are eventually resumed in the general 

 bristling of the spines, proves that this general communication between 

 the spines is maintained by the direct conductility of the supposed 

 internal plexus, and is not of the nature of a reflex action, in which the 

 nerve ring is concerned as a general centre for the responsive, as distin- 

 guished from the co-ordinated, action of the spines. 



These results taken together prove that all parts of the nervous 

 svstem of the Echinodermata are, in function as in structure, both 

 central and peripheral, although the nerve-ring exercises a larger 

 share of centralising influence than does any other part of the system. 



