638 A. A. W. HUBREOHT. 



of superficial metameric connections (Ransom and d'Arcy 

 Thompson, vide supra) as well as of this set of deeper 

 connections between the transverse and the latero-longitu- 

 dinal nerve- stems (n. lateralis and n. pneumogastricus, of 

 Petromyzon would thus be a remarkable repetition of the 

 similar arrangement in the Nemertea, as it has been here for 

 the first time demonstrated. 



The facts as they lie before us do not, however, admit of 

 any very circumstantial comparison so far as the nerves in 

 particular are concerned, and I purposely refrain from entering 

 into any details. Yet it should be remarked : 



(1) That the polymerous root of the Vertebrate vagus nerve 

 is very readily explicable if we take the Nemertean arrange- 

 ment as a starting-point (PI. XLII, figs. 1, 2, vag), as is also 

 the mixture of sensory and motor elements in this root.^ 



(2) That similarly, if the anterior cephalic nerves (e. g. the 

 fifth) should pi'ove to be polymerous, this would in no way be 

 astonishing nor difficult to bring into harmony with that same 

 starting-point. 



(3) That the presence of superficial branches to the integu- 

 ment and to the musculature, and of deeper branches to the 

 intestinal epithelium in those parts that will contribute to 

 form the cephalic nerves, is similarly foreshadowed in the 

 Nemertea. 



(4) That the equivalent of the Nemertean vagus nerve will 

 have to be sought for in such branches of the Vertebrate vagus 

 as move especially innervate the intestinal epithelium,^ whereas 



1 Rohon, " Ueber den Ursprung des Nervus vagus bei Selachiern," ' Arbeit. 

 Zool. Inst. Wien/ vol. i, p. 159, 



2 I have good reasons, based upon actual observations made by my pupil, 

 Mr. Dobberke, to believe that the ramus intestiualis vagi in adult Elasmo- 

 branchs may be traced centripetally from its region of innervation of the 

 foremost portion of the intestinal wall, towards the brain, as a bundle of nerve- 

 fibres running parallel to and combined with those for the branchial apparatus, 

 but that, nevertheless, this bundle can be separately traced up to the vagus 

 ganglion, without any further intimate relation to those branchial branches 

 (cf. Beard, loc. cit., p. 110). If this should actually be the case, the 

 possibility of a direct comparison between the Nemertean 



