570 



S.O.). From the thickeiiiug cells are given off for some time until 

 a large ganglionic mass is formed, which still for some time remains 

 fused with the skin. 



In fact, in the case of the mesocephalic ganglion, the mode of 

 development is well marked, and easy to study. The sensory thickening 

 soon begins to grow forwards over the snout, and as it does so the 

 ganglion begins to leave the skin. As this takes place a nerve is 

 developed from the thickening ' ), and connects the ganglion with its 

 branchial sense organs. 



From its course, relations, etc. this nerve is seen to be the oph- 

 thalmicus profundus 2). 



It is morphologically the suprabranchial nerve of the second 

 segment. 



The distance between the mesocephalic and Gasserian ganglia, 

 even in early stages, is very short. The outgrowth from the ridge 

 which forms the main stem of the mesocephalic ganglion is practically 

 continuous with the outgrowth which forms the main stem of fifth. 

 VAN WiJHE has also drawn attention to this. 



In later stages the connection becomes a common one in that the 

 main root of the mesocephalic ganglion fuses with the roots of the 

 Trigeminus, and the mesocephalic ganglion itself fuses with the Gasserian 

 ganglion. A stage in which this fusion is not quite complete is shown 

 in fig. 3 where the mesocephalic ganglion M.G. is very nearly ab- 



— iV. 



'G.G. 

 M.G.''' 



V 



\ 

 » 



0. 



Fig. 3. Part of horizontal section. Acanthias. Shows fusion of 

 mesocephalic M-g. and Gasserian ganglion G.G. N. notochord. O. eye. 



1) On this point I still hold and indeed extend my opinion to many 

 other nerves. I regret to see that on this matter I must disagree with 

 Prof. Feobiep. 



2) Also VAX WijHE op. cit. 



