NOTES ON THE DEVELOPMENT OF THE NEWY!. 581 
neural ridge, but states that they become detached later from 
the spinal canal, and subsequently joined to it by the dorsal 
and ventral roots. Bedot (5) states that in the Newt the 
connection is never broken, and our researches lead us to agree 
with him on this point. 
Hoffmann (12) describes the spinal nerves in Teleosteans as 
growing from a neural ridge, but appears to think that the 
cranial nerves, which arise before the neural canal is closed, 
are, partially at least, derived from the adjacent epiblast. 
O. Hertwig (10), in a few scattered observations on the 
spinal nerves of the Frog, is inclined to support His’ view. 
More recently the theory of the derivation of the whole or 
greater part of the cranial nerves from the epiblast has been 
supported by Mr. Spencer (21) and Mr. Beard (4). This view 
is a revival of that held by Gétte (9). Mr. Spencer asserts 
that the whole nerve, including root and ganglion, is, in the 
Frog, split off from the nervous layer of the epiblast. If this 
be so, all the branches must ultimately be derived from the 
same source. Mr. Beard confirms him in this statement, and 
figures one section showing a thickened mass of epiblast con- 
tinuous dorsally with the still open neural canal, but there is 
nothing to show that this thickening becomes a nerve. Such 
a split, as is figured between it and the external layer of epi- 
blast, very often occurs in imperfectly preserved specimens. 
We find no such thickenings in Newt embryos of similar 
stages, a typical section of which is shown in fig. 15, and our 
observations on the Frog lead us to doubt the accuracy of Mr. 
Spencer’s account. We have attempted to show that it is, at 
all events, not universally true for Amphibia, as Mr. Beard 
assumes. 
Mr. Beard has described in Elasmobranchs (4) a fusion of 
the typical cranial nerve with the sense organ of its segment. 
This corresponds with the dorsal fusions found by us in the 
Newt. The ventral fusion of the nerve with the gill-cleft, as 
described above in the Newt, corresponds to the second fusion 
found by van Wijhe in Elasmobranchs (22), and to the ventral 
fusion found by Froriep in Mammals (7). Mr. Beard considers 
