130 W. BALDWIN SPENCER. 
Section 19, which is taken from an axolotl, shows the same 
proliferation, and also that this is greatest at the level of the 
lateral line. In course of development the string of cells thus 
formed becomes gradually separated off from the nervous layer 
of the epidermis, which retains its normal thickness of one cell 
and for some time afterwards the exact boundary of the nerve 
is ill-defined, while the mesoblast grows in between it and the 
epiblast, the only point at which it remains connected with the 
latter being that at which the Gasserian ganglion is developed. 
This is seen in section 17, where the main strand of the tri- 
geminal is seen separated from the epiblast, while in fig. 18, a 
slightly more anterior section, the Gasserian ganglion is yet 
connected with the epiblast ; in fig. 17 the nerve should be 
represented as lying somewhat nearer to the surface. 
In further development the whole nerve and ganglion comes 
to hie within the mesoblast, and, as seen in fig. 20, the latter 
quite loses its connection with the epiblast. 
This development of the ganglia at the level of the lateral 
line, and the fact of their long connection with the epiblast at 
this point, when all the rest of the nerve has been separated 
off, is of great interest in connection with certain points in 
the development of the Elasmobranch nerves to be shortly 
noticed. 
With regard to the development of roots, I hope to be able 
soon to publish some detailed account. At the earliest period 
at which they can be recognised they appear to arise from the 
dorsal summit of the brain, and, as shown in figs. 16 and 19, 
to originate by proliferation from the nervous layer, which 
afterwards separates entirely from the brain, and can be traced 
running right across the head dorsally. 
In the region of the trunk, a considerable period after the 
cranial nerves are well formed and recognisable, there seems 
to be no development of spinal nerves, though the nervous 
sheath is clearly developed, and in this the lateral line. 
Through the kindness of Dr. Beard I have been enabled to 
examine several beautiful series of sections of Elasmobranch 
embryos, and he has also allowed me to introduce into this 
