222 



In certain of the figures a number of cells forming the rudiment 

 of the olfactory ganglion are drawn in intimate connection with the 

 epiblast thickening Avhich forms the olfactory pit (Fig. 19 and 20), 



It has been stated above that the nerve connecting any cranial 

 segmental ganglion with its corresponding segmental sense organ is 

 derived from the skin. This is also the care with the nerve connecting 

 the compound vagus ganglion with the various segmental sense organs 

 of the trunk, — that is, the so-called lateral nerve. This mode of ori- 

 gin was ascribed to it by Semper, Goette, van Wijhe and Hof- 

 mann. My former account in which I supported Balfour's view is, 

 at any rate in part wrong. 



In my former note ^ I put forward the view that the auditory 

 nerve was merely a modified segmental sense organ, and as a natural 

 corollary to this that the auditory nerve was a segmental nerve (poste- 

 rior root.) The latter view, though not directly stated, was a natural 

 inference. I however overlooked the fact that van Wijhe^ had fur- 

 nished independent evidence for regarding the aiiditory nerve as a 

 segmental nerve, he did not however hint at any morphological con- 

 nection between the auditory organ and segmental sense organs. 



I was further unaware of a paper of Mayser's^ (for a knowledge 

 of which I have to thank Prof. Wiedersheim) in which among other 

 things the conclusion is drawn that the segmental sense organs, so- 

 called »Schleim-Canale« form an accessory auditory organ. This view 

 is based upon the close connection in the brain of the auditory centre 

 and centre of origin of the nerves supplying these sense organs. 



The olfactory nerve has been classed among the segmental nerves 

 by Marshall", who has furnished a good deal of evidence for such a 

 conclusion. If the probability of the olfactory ganglion arising like the 

 other cranial ganglion as a proliferation of the epiblast, be converted 

 into a certainty, then while accepting fully Prof. Marshall's view of 

 the segmental nature of the Olfactory nerve, the question will have to 

 be considered whether the sense organ which arises in connection with 

 the olfactory ganglion is not the homologue of the sense organ which 

 arises with any other cranial ganglion — that is the homologue of a 

 segmental sense organ. 



3 Zool. Anzeiger 1884. No. 161—162. 



* Van Wijhe, Über die Mesodermsegmente und die Entwicklung der Nerven 

 des Selachierkopfes. Amsterdam, 1882. 



5 Mayscr, Vergleich. Anat. Studien über das Gehirn der Knochenfische etc. 

 Zeitschr. f. wiss. Zool. 36. Bd. p. 259. 



6 Op. cit. 



