NERVOUS SYSTEM OF ANTEDON EOSACEUS. 643 



du tronc nerveux se divisant de cette maniere, il y aura, re- 

 pandu a la surface du corps, un systeme nerveux p^ripherique 

 extremement developpe^ fournissant des nerfs aux radioles, aux 

 pedicellaires, aux clavicles des fascioles, et en general a toutes 

 les parties externes." 



Fredericqi was led, from a series of experiments on Echinus 

 and Toxopneustes, to suspect the existence " d'un plexus ner- 

 veux situe dans Tepaisseur de la peau qui recouvre le test h 

 I'exterieur," but did not succeed in demonstrating its existence 

 anatomically. 



More recently Romanes and Ewart~ have described experi- 

 ments on living Echini, which lead them to believe in the 

 existence not only of an external nerve plexus outside the test, 

 but also of an internal plexus on its inner surface ; they fur- 

 ther believe that the two systems are connected by nerve- 

 fibres running through the plates of the test. The external 

 plexus they figure^ and describe " as lying almost immediately 

 under the surface epithelium, and extending from the shell 

 to the spines and pedicellariae ;" and in a postscript they 

 state that they " have been successful in obtaining full histo- 

 logical demonstration of the internal nervous plexus of 

 Echinus," and promise full descriptions of " its character, dis- 

 tribution, and mode of communication with the external 

 plexus." * 



Concerning Holothurids, both Krohn and Baudelot describe, 

 in the memoirs cited above, branches from the radial nerves to 

 the tube feet. More recently Hamann,^ in the paper already 

 quoted, has added valuable details concerning the distribution 

 of these branches. He shows that the branches to the tube 



' Fredericq, " Contributions a I'etude des Echiuides," ' Arcliives de Zoologie 

 Experiraeutale,' tome v, 1876, p. 438. 



^ Romanes and Ewarfc, " On tlie Locomotor System of Echinodermata," 

 'Phil. Trans.,' 1881, part iii. 



^ Romanes and Ewart, loo. cit., p. 836, pi. 80, figs. 16 — 18. These figures 

 are very different to Loven's, wliich, however, were drawn from another 

 genus. 



•* Loo. cit., p. 882. 



* Hamann, loc. cit., p. 168, and pi. ii, figs. 51, 52, and 53. 



VOL. XXIV. NEW SER. O O 



