PIFFERENTIATIONS OF ECTODERM IN NECTURUS. 547 
Fie. 22.—Section through the ramus buccalis as the trigeminal and facial 
parts diverge. 
Fic. 23.—Section through the distal part of the post-trematic branch of the 
glosso-pharyngeus. 
Fic. 24.—Section through a sense-organ in the ventral part of the hyo- 
mandibular line, as the nerves begin to form. 
Fig. 25.—Section through the skin above the ear. 
Fic. 26.—Section showing the innervation of the supra-orbital sensory 
ridge by united branches from the trigeminal and facial nerves. 
PLATE 37. 
Fic. 27.—Section through the second brachial ganglion, showing six of the 
motor nerves that supply the adjacent myotome, which the section cuts above 
aud below, as it curves around the ganglion. 
Fies. 28 and 29.—Sections through dorsal sensory nerves of the trunk. 
The arrow in Fig. 29 shows the direction of the main stem. 
Fic. 30.—Section showing the distal distribution of branches from the 
ramus hyomandibularis vit. 
PLATE 38. 
Fic. 1.—Embryo 12 mm. long, with ectodermic ridges reconstructed, and 
the position of the anterior ganglia indicated. 
Fig. 18.—Embryo 13 mm. long, with the ectodermic ridges reconstructed, 
and the position of the anterior ganglia and lateral line nerves indicated. 
Fic. 21.—Embryo 15 mm. long, showing the ectodermic ridges and sense- 
orgaus of the lateral line. Rudiments of the external gills have appeared, and 
the peripheral nerves begin to develop. Facial, vagus, and lateral line nerves 
are given in red; the trigeminal and glosso-pharyngeal nerves in black. 
Fic. 31.—Embryo 19 mm. long, showing the anterior sense-organs of the 
lateral line system, and their innervation from the ventro-lateral surface. The 
external gills and fore-limb are removed. The nerves are coloured as in 
Fig. 21. 
Fic. 32.—Embryo at the same stage of development as in Fig. 31. The 
distribution of the sense-organs on the trunk is given, and the present pig- 
mentation of the embryo indicated. 
Fic. 33.—Head of an embryo at the same stage as Figs. 31 and 32, showing 
the distribution of sense-organs on the head, the dorsal surface of which is 
now quite evenly pigmented. 
