BRANCHIAL SENSE ORGANS OF ICHTHYOPSIDA. 221 



Fig. 15. Fifth nerve fused with its sensory thickening (p.br.s.o.), and 



proliferation of Gasserian ganglion from the skin. G.gl. 



Gasserian ganglion. T. ocellata. Z. c, oc. 2, cam. Inc. 

 Fig. 16. Similar figure to preceding one. T. ocellata. Z. c, oc. 2, 



cam. luc. 

 Fig. 17. Section through hind- and fore-brain. Shows Gasserian 



ganglion just before its separation from the skin. T. 



ocellata. Z. a, oc. 2, cam. luc. 

 Fig. 18. Small piece of a horizontal section of a Torpedo embryo. 



Shows hyoid prse-branchial nerve (pb.n.) lying in epiblast 



and not yet separated from it. G.gl. Gasserian ganglion. 



f.gl. Facial ganglion. 



Plate VIII. 



Fig. 19. Transverse section through hind-brain of a Torpedo embryo. 

 Facial nerve (vn) just on point of fusion with its sensory 

 thickening. Gill-cleft (hyoid) just about to form. Z. c, 

 oc. 2, cam. luc. 



Fig. 20. A similar section. Facial nerve just fused with skin, and its 

 post-branchial (p.n.) passing on to muscles of cleft. Z. a, 

 oc. 2, cam. luc. A later stage of facial ganglion in fig. 42. 



Fig. 21. Facial ganglion leaving skin, and still connected by two 

 supra-branchial nerves (s.b.n. 1, and s.b.n. 2). Z. d, oc. 2, 

 cam. luc. 



Fig. 22. Horizontal section of a Torpedo embryo. Facial ganglion 

 fused with auditory, but line of demarcation is obvious. 

 Facial has just left the skin, and is leaving a supra- 

 branchial nerve (s.b.n.) behind it. 



Fig. 23. Part of a transverse section through the auditory region of a 

 Torpedo embryo. Auditory nerve (vm) not yet fused 

 with auditory thickening (au.o.). Z. f, oc. 2, cam. luc. 



Figs. 24 & 25. Auditory just fused with auditory thickening, and 

 ganglion proliferating. Letters as before. T. ocellata. 

 Z. f, oc. 2, cam. luc. 



Fig. 26. Low-power drawing of a horizontal section, such as the two 

 preceding figures form part of. 



Fig. 27. Transverse section, rather oblique, through hind-brain of a 

 frog embryo. Shows auditory nerve and thickening on one 

 side, and vagus nerve and ganglion on the other, au.n. 



