BRANCHIAL SENSE ORGANS OF ICHTHTOPSIDA. 191 



given above seem to me to confirm Dohrn's 1 conclusion that the mouth 

 arose from a pair of coalesced gill-clefts. 



Second Segmental Nerve — Ophthalmicus Profundus, Ciliary 

 Ganglion, and Radix Longa. , 



A good deal of confusion exists as to the actual nerve components 

 of this segment. 



Marshall 2 regards the motor oculi as the main stem of the ciliary- 

 ganglion, and attributes to it the character of an anterior and posterior 

 root. In Marshall and Spencer's 3 paper the ophthalmicus profundus is 

 also classed as part of this segment. Schwalbe 4 had previously shown 

 that the ciliary ganglion was really the ganglion of the posterior root 

 of this segment, a demonstration which Marshall confirmed embryo- 

 logically. Following on and extending these discoveries, Van Wijhe 

 recognised the most important component of this segment in the 

 ophthalmicus profundus, which he classed as the posterior root of the 

 segment. While accepting to a certain extent Van Wijhe's view, I 

 feel bound to admit that from Van Wijhe's researches alone, the 

 matter does not stand in a very clear light. 



Here, as in other cases, Van Wijhe's preconceived notions as to the 

 correspondence of the roots of cranial nerves to those of the spinal 

 nerves, interfered with the proper interpretation. Marshall 5 first gave 

 an account of the development of the ciliary ganglion ; this account 

 Van Wijhe added to, but it is still by no means complete. And 

 although the development of no cranial ganglion is easier to follow, 

 and no fusion of the epiblast more obvious than the development and 

 fusion of the ciliary ganglion, this fusion has never before been figured, 

 and Van Wijhe's earliest stage figured (fig. 31,gl.c, op. cit.) is a stage 

 at which the ganglion is in great part separated from the skin, and in 

 which the ophthalmicus profundus which runs from the ganglion along 

 the snout and forms the supra-branchial branch, has just begun to 

 develope. 



A glance at the diagrams (figs. 45 and 46) of the cranial nerves, 

 according to my views, will simplify matters and pave the way for the 

 account shortly to be given. 



1 Dohrn, "Studien, &c," No. 1, 'Mittheil. a. d. Zool. Station zu Neapel,' Bd. iii., p. 252. 



2 Marshall, "Segmental Value of Cranial Nerves," ' Journ. of Anat. and Physiol.,' 1882, 



3 Op. cit., p. 29. 



4 Schwalbe, 'Das Ganglion Oculornotorii. ' 



5 Marshall, " Head Cavities and Associated Nerves, &c," ' Quart. Journ. Micr. Sfr.,' 1880 



