278 SCOTT. ' [Vol. I. 



from an epiblastic thickening immediately behind the lens 

 invagination, a statement which I can confirm. It is, at first, 

 apparently single, but soon divides into two parts (Figs. 39, 40, 

 and 41, PI. XI), one of which lies above the optic vesicle and 

 belongs to the ophthalmic branch, while the other gives rise to 

 the maxiliary and mandibular branches. I have not observed 

 any connection between the Gasserian and the ciliary ganglia. 



7. The Facial Nerves. — Much dispute has arisen of late 

 as to the distribution of the seventh pair, and its history, there- 

 fore, needs to be examined with especial care. The facial 

 nerve arises at about the same period as the trigeminal as an 

 outgrowth from the hind-brain, which fuses with a thickening 

 of the skin, the future ganglion. According to Shipley this 

 ganglion is at first continuous with the Gasserian, but this stage 

 I have not seen ; its connection with the skin is, however, plain. 

 The main trunk of the nerve soon divides into three branches, 

 one of which, the ramus reciirrens, passes backward beneath 

 the auditory vesicle. Shipley states that in young larvae no 

 connection exists between this recurrent branch and the vagus, 

 nor have I succeeded in finding it. It probably is brought 

 about at a comparatively late stage of larval development. Of 

 the other branches of the facial the posterior passes down be- 

 tween the first and second gill-clefts, while the anterior arches 

 over and runs down in front of the first cleft, which later gives 

 rise to the ciliated circumoral ring. 



Marshall and Spencer (23) have described the formation of 

 a secondary root and atrophy of the primary root of the sev- 

 enth nerve in the case of Scylliiun. Fig. 42, PI. XI, shows a 

 somewhat similar process taking place in the yo\xx\'g Ammoccetes, 

 where two distinct roots, a dorsal and ventral, connect the brain 

 with the facial ganglion. I have, however, seen nothing which 

 suggests an atrophy of the dorsal root, and judging from the 

 origin of the facial in the adult, it is very unlikely that the ven- 

 tral root, seen in Fig. 42, can become the permanent root of the 

 seventh. Wiedersheim (41) and Ahlborn have shown that in 

 Petromyzon the auditory nerve has a double origin, and not 

 improbably the ventral strand passing to the facial ganglion 

 may eventually become one of these. 



Julin (see Van Beneden, 40) has stated that in Ammocoetss 

 the seventh nerve supplies the first permanent {i.e., second) 



