282 SCOTT. - [Vol. I. 



direction taken by those branches of the glossopharyngeal 

 is somewhat, but not essentially, different from that seen in 

 the vcr}' young larva; ; a change which is brought about by the 

 shifting of the entire branchial apparatus posteriorly. In the 

 embryo and young Ammocoete the hyobranchial (first perma- 

 nent) cleft is situated immediately beneath the auditory vesicle 

 (Figs. 3 and 5, PI. VIII), while in the adult the branchial basket 

 has become greatly extended and shifted backwards, so that the 

 first (permanent) cleft comes to lie distinctly posterior to the 

 ear-capsule. The nerves, of course, follow this shifting, and 

 the anterior branch of the ninth nerve now passes downwards 

 and somewhat backwards, instead of forwards, as in the embryo. 

 In the stage shown in Fig. 40, PI. XI, there would seem 

 to be two distinct vagus ganglia connected with the brain by 

 three, or perhaps four, roots, and it is noticeable that these roots 

 are relatively much more widely separated than in the older 

 larvae or the adult, as figured by Wiedersheim and Ahlborn. 

 From these ganglia the branchial nerve for the six posterior 

 gill-clefts proceeds, and shows a ganglionic swelling between 

 each pair of clefts. Whether these ganglia contain any ele- 

 ments derived directly from the epiblast of the skin, I was 

 unable to determine. The most noticeable fact about this stage 

 in the development of the vagus group is the great concentra- 

 tion of its elements as compared with the stage shown in Fig. 

 36, PI. IX; and later stages still further increase this concentra- 

 tion, and the two vagus ganglia coalesce into a single one {i.e., 

 assuming that these two ganglia really belong to the vagus, as 

 there is every reason to believe). The lateral nerve is exceed- 

 ingly small, and, as Langerhans (22) showed, peculiar in posi- 

 tion, being placed very high up towards the median dorsal line, 

 a peculiarity which is seen from the first appearance of the nerve. 

 I believe I have traced the origin of this nerve from a progres- 

 sive differentiation of the epiblast, beginning in the region of 

 the vagus ganglia and proceeding posteriorly. This takes place 

 in the later embryonic stages, but I have not demonstrated the 

 process completely to my satisfaction. At all events, the lateral 

 nerve is unmistakably present very shortly after hatching, a 

 much earlier period than Shipley has supposed, as from its 

 minute size one may very easily overlook it. It is best seen in 

 transverse sections, and lies close to and just above the spinal 



