580 ALICE JOHNSON AND LILIAN SHELDON. 
the sense organ (fig. 34), and the ventral portion of the main 
trunk divides into two branches, the post-branchial (fig. 35) 
behind the second gill-cleft, and the pre-branchial (fig. 33) in 
front of it. 
The Vagus arises from the brain in the same manner as 
the other cranial nerves, but we have not traced its further 
development. 
DEVELOPMENT OF NERVES IN THE FROG. 
We have made a few observations on the development of 
the nerves in the Frog in some series of sections cut by Mr. 
Durham, and very kindly lent to us. . Our observations, as far 
as they extend, confirm in every respect what we have described 
in the Newt. A neural ridge is formed on the dorsal surface 
of the medullary canal after it has separated from the epiblast, 
as shown in fig. 30, representing part of a transverse section 
through the hind region of the trunk of an embryo. In this 
embryo the neural ridge extended through the trunk, but was 
less distinct in the head, where the nerves had begun to form 
as outgrowths from it. Fig. 29 shows the origin of the facio- 
auditory nerve. Its small size shows that it must be at a very 
early stage. It is growing on each side from the dorsal surface 
ofthe brain towards the auditory vesicle, which is beginning 
to develope from the inner layer of the epiblast. It seems to 
us that the whole appearance is inconsistent with the view 
that the nerve has split off from the epiblast, as Mr. Spencer 
asserts (21). 
HistToRIcAL AND CRITICAL. 
Our observations are, on the whole, consistent with the 
account of the derivation of nerves first put forward by Pro- 
fessor Balfour in 1876 (1), afterwards confirmed by Professor 
Marshall in other types, and since generally accepted. They 
do not lend any support to the peculiar view of His, as to the 
presence of a “ Zwischenstrang”’ (11). 
Sagemehl (18) derives the spinal nerves in the Frog from a 
