DIFFERENTIATIONS OF ECTODERM IN NECTURUS. 539 
skin with the underlying tissues in a region not specially 
sensory. 
Fig. 30 shows a later stage in the development of the hyo- 
mandibular nerve, when the forest of tiny fibres seen in 
fig. 24 has been swept into bundles connected with the nerve. 
On the lateral lines of the trunk the fibres formed in the 
deeper protoplasm of the ectoderm do not at first penetrate 
the limiting membrane that bounds the inner surface of the 
skin, but become gathered into a nerve before leaving the 
ectoderm, thus giving rise to the nerve in the manner described 
by Dohrn (8). 
The branchial, pharyngeal, and palatine nerves have rela- 
tively fewer cells, and are chiefly formed by outgrowths from 
the ganglion, yet cells from the ganglion also migrate into 
these nerves. Pl. 36, fig. 23, shows the distal part of the 
glosso-pharyngeus, and, for the relative number of cells, may 
be compared with the ophthalmicus superficialis (fig. 26), 
the buccalis (fig. 22), or the distal hyomandibularis (PI. 
37, fig. 30). 
The beginning of the motor spinal nerve has been described. 
The distribution of its branches to the muscle plate is peculiar. 
As has been described in other Amphibia, the motor fibres of 
the spinal nerves pass directly through the ganglion. Fig. 
27 gives a section through the fourth spinal, second brachial, 
ganglion. The muscle plate is cut above and below as it 
curves over the outer surface of the ganglion, and the section 
shows six motor nerves on their way to the muscle plate. 
These are not the only or even the main motor nerves of the 
segment, but the section serves to illustrate the irregularities 
that occur in the distribution of the spinal motor nerves. 
Figs. 28 and 29 show two sensory spinal nerves that underlie 
the skin on the dorsal surface of the embryo. The structure 
of the nerves suggests the formation of nerves in the tail of 
the frog as described by Hensen (19). The nerves run longi- 
tudinally, and are connected with the ganglion by a nerve that 
passes through the dorsal part of the muscle plate to the sur- 
face of the embryo. The cells forming these dorsal nerves do 
