566 



beyond those already known. But I do not exaggerate when I say 

 that every observer who has worked on the subject from Schwalbe 

 onwards to Hoffmann has either fallen into error, or made statements 

 or used terms which were calculated to lead others astray. The de- 

 sirability of a further examination of the matter led me to spend some 

 time in studying the nerves concerned, and in endeavouring to find out 

 exactly what each observer meant in his descriptions of his work. 

 My task was very materially assisted by Prof. Wiedersheim's kindness 

 in placing a fine series of Acanthias embryos at my disposal. 



In a former paper i) I described the early development of a 

 ganglion in the region of the mid brain, and, following everyone who 

 had worked on the subject, I called it the ciliary ganglion. Except 

 in the name applied to it, the account there given of its early deve- 

 lopment is correct. But I committed the error, in order to harmonise 

 Marshall's^) and van Wijhe's^) researches on older embryos of Elas- 

 raobranchii, of ascribing the radix longa to it. The ganglion there des- 

 cribed has nothing to do with the radix longa in the sense I imagined. 

 VAN WijHE*) has also given a partial account of this ganglion, which 

 was described and partially investigated by Marshall^), van Wijhe 

 following Marshall also called it ciliary ganglion but was quite clear 

 that it was not homologous with the Ciliary ganglion of higher forms. 

 This ganglion which has been called ciliary by Marshall, van Wijhe, 

 Schwalbe'^), Dohrn, myself and others I shall, for reasons to be given 

 shortly, describe as the mesocephalic ganglion. It is the ganglion of 

 the ophthalmicus profundus, as van Wijhe first clearly demonstrated. 



Marshall '), as mentioned above, first fully described the meso- 

 cephalic ganglion which he regarded as the Ciliary ganglion of adult 

 Vertebrates. This view was cordially endorsed by Schwalbe^), who 

 endeavoured to show that the ciUary ganglion of adult Vertebrates 



1) Beakd. The System of Branchial Sense organs and their associated 

 ganglia in Ichthyopsida. Quart. Jour. Micros. Sei. 1885. Vol. 26. p. 25. 

 (of reprint.) 



2) Marshall. The Head Cavities and their associated nerves in 

 Elasmobranchs. Quart. Jour. Micros. Sei. Jan. 1881. 



3) VAN Wijhe. Über die Mesodermsegmente und die Entwickelung 

 der Nerven des SelacMerkopfes. Natuurk. Verb, der Koninkl. Akademie, 

 deel XXII. 



4) op. cit. p. 20. 



5) op. cit. 



6) Schwalbe. Das Ganglion oculoraotorii. 



7) Marshall op. cit. 



8) Schwalbe op. cit. p. 3. 



