636 A. A. W. HUBREOHT. 



earlier stage^ still permanent in the Nemertea, where the 

 metamerically consecutive transverse nerve-tracts similarly 

 unite the medullary nerve and the lateral stems. 



This connection is, as we know, also brought about in the 

 Nemertea by the plexus, in those parts of it which spread out 

 between the transverse tracts, and it may here be asked if 

 relics of such a plexus between the successive precursors of the 

 spinal nerves are perhaps retained, not only in Amphioxus 

 (see above, p. 625, and Rohon, loc. cit., fig. 13), but also in 

 Osseous Fishes, in the numerous superficial nerves described 

 and figured by Stannius,^ or whether we must rather look 

 upon this multiplication of lateral nerves (one of which is 

 called by Stannius the nervus lateralis trigeraini, others, rami 

 communicantes of the dorsal branches of spinal nerves, &c.) 

 as derivatives from the nervus lateralis vagi.^ This question 

 can, of course, only be solved by careful anatomical and 

 embryological investigations. That the nervus lateralis was 

 often (Stannius) observed in the Petromyzontidse only along 

 a part of the length of the body (Schneider and Born, ac- 

 cording to Ahlborn,^ observed it as " bis an das Hinterende 

 des Korpers'^) is not confirmed by modern investigators. 

 Ahlborn's description (loc. cit., p. 304) of the variable 

 situation of this nerve in Petromyzon is very suggestive 

 in connection with the views here advocated. E-ansom and 

 d'Arcy Thompson consider that the regularity of the in- 

 tegumentary sensory apparatus is not yet established in 

 Petromyzon, as may be concluded from the citation given 

 above. 



We have now considered the superficial ramifications of 

 what I may call the lateral nerve-system, both in lower worms 

 and in Vertebrates; we must now turn to the intestinal, to 



1 ' Das periplierische Nerveusystem der Fisclie,' 1849, pis. ii — iv. 



^ It should be remembered that Beard is inclined (loc. cit., p. 139) to look 

 upon the superficial longitudinal nerve-fibres, bj which the successive epithelial 

 modifications along the lateral line are often connected (Solger, Bodenstein), 

 as such derivatives (by longitudinal fission in its very early stages) of the 

 nervus lateralis. 



3 'Zeitschr. f. wiss. Zool.,' Bd. xl. pp. 303 and 301. 



