98 JOHN BEARD. 
of the cranial nerves, which are morphologically as well as 
physiologically inseparably connected with the former. 
It would take up too much time and space to give here a 
history of all the researches on these two sets of organs, which 
have hitherto been usually treated apart from each other as if 
they had no connection. 
The work has been mainly carried out on embryos of Tor- 
pedo ocellata, for which I have to thank the Zoological 
Station at Naples. But I have also studied Teleostei and 
Amphibians, and have had a few embryos of Mustelus and 
Pristiurus. However, in the descriptions in the following pages, 
unless otherwise stated, the condition of affairs in Torpedo will 
be understood to oe under discussion. 
In the first place, I think it will be of great advantaee and 
will tend to simplify matters very much if the general schema 
of the development of a cranial nerve (dorsal root) of an 
Elasmobranch, such as Torpedo, be given. 
Then those cranial nerves, which I regard as segmental, 
will be discussed: olfactory, nerve of ciliary segment, tri- 
geminal, facial, auditory, glosso-pharyngeal, and vagus. 
The optic nerve is left entirely out of consideration. Firstly, 
because I have made no investigations, and hence have no new 
facts about it to record; and secondly, as is well known, its 
whole development is different from that of the other cranial 
nerves ; and I can only agree with those zoologists who class 
the optic nerve entirely apart from the other cranial nerves. 
Not so, however, with the olfactory and auditory nerves and 
organs. Partly following Marshall, I feel bound to place these 
nerves in the category of cranial segmental nerves, and to 
class the olfactory and auditory ae as specialised branchial 
sense organs. 
Finally, after the account of the various nerves, the bearing 
of the facts described on the morphology and ancestral history 
of Vertebrates will be discussed. 
1 Beard, “On the Segmental Sense Organs, &c.,” ‘ Zool. Anzeiger,’ 161, 
162, 1884; also, On Cranial Ganglia, &.,” ‘Zool. Anzeig.,’ 192, 1885. 
