EELATION OF THE NEMBRTEA. TO THE VERTEBEATA. 619 



that give a clue to the possible action of natural selection in 

 the gradual evolution of metamery. This clue appears to me 

 to be far more distinctly contained in the views here advocated 

 than in the other hypotheses. 



It may further be remarked, now that we have once more 

 alluded to Bateson's phylogeny of the Chordata, that even 

 this naturalist does not feel justified in wholly rejecting 

 the Nemertea from the Vertebrate pedigree. Whilst in the 

 text of his article (loc. cit. p. 566) he does seem to prefer 

 this negative alternative ; still, in the subjoined diagram of the 

 general relationships of Urochorda, Hemichorda, Cephalo- 

 chorda, and Vertebrata, the Nemertea are introduced — with a 

 point of interrogation, however — as a side branch lower down 

 on the common parent stock. Now, this being concordant 

 with my own views of the Chordate phylogeny, — the point of 

 interrogation excepted, — it is necessary to inquire why there 

 is this discrepancy between Bateson's speculations in the body 

 of his treatise and the hypothetical pedigree at the end of it. 

 It appears to me that this is due to his hesitation (loc. cit. 

 p. 555) in accepting the views hitherto entertained and advo- 

 cated by myself as to the phylogenetic connection between the 

 Nemertean and the Vertebrate nervous system. For this hesi- 

 tation Bateson has good reasons, and while I appreciate the 

 soundness of them, I hope in the remainder of this chapter to 

 remove the reluctance of him and others to accept the phylo- 

 genetic significance of the Nemertea, thanks to new light that 

 may be thrown on the evolution of the central nervous system 

 of the Chordata by the observations recorded by me on the 

 nervous system of the " Challenger " Nemertea. 



It is to these speculations on the nervous system that we 

 now have to turn our attention. 



As will be seen from the terminology introduced in the 

 paragraph on the nervous system in my Report on the "Chal- 

 lenger " Nemertea, and as it is now time more fully to develop, 

 I am inclined to attach considerable morphological importance 

 to the arrangement of the diflFerent constituent parts of the 

 nervous system in the Nemertea. In former publications I 



