294 
Without dogmatising on the matter it may be stated that the 
development of ganglion cells and of nerve from the lateral line neuro- 
epithelium appears to be a somewhat simplified paradigm of what takes 
place in the central nervous system itself. 
It is not easy to choose a starting point for the description of 
observations covering so extensive a field as those which have recently 
engaged my attention. Still less do the notes of the investigation of 
sections of about 100 Raja embryos ranging in size from 3 or 4mm 
to 19 cm admit of condensation into the limits required by this jour- 
nal. There is, moreover, great advantage to be gained from of a 
description of actual sections, followed by a summary, but in this place 
the latter alone can be given. 
A rational account might begin with a description of the deve- 
lopment of the central nervous system, and, in such a case, the tran- 
sient ganglion cells, as the first formed ganglionic elements, would 
require almost primary attention '). Three years ago, with the material 
then in my possession, such an account would have appeared easy 
— I knew nothing then of the remarkable appearances presented by 
these cells in Raja-embryos, and only after the investigation of this 
genus was it possible to pierce the clouds which enshrouded them in 
Lepidosteus and to find essentially the same conditions there also. 
a) Histogenesis of the lateral line and nerve. 
As the lateral line and nerve etc. form the simplest case, for in 
dealing with it we have to do with a detached piece of neuroepithe- 
lium from which there arises only one kind of nerve and one kind of 
ganglion cell, it may receive first attention. 
There is little reason why the matter should be dealt with in 
detail, although the facts which can be learnt from its development are 
of the highest importance for the elucidation of problems connected 
with both the morphology ?) and the histogenesis of the central nervous 
system. As far as it goes, the account given in my 1885 paper 
(pp. 18—25) can still be maintained. The “suprabranchial” *) position of 
the original bit of neuroepithelium, its mode of growth backwards, the 
1) At the time of final revision of the present paper an accouut of 
these cells was already in the press. Some former preliminary statements 
of mine on the early development of the central nervous system may be 
also referred to (Anat. Anz. 1888). 
2) See “The Interrelationships of the Ichthyopsida”, Anat. Anz., 1890, 
p. 154. 
3) The terms supra-, post- and praebranchial were proposed to replace 
van WısHe’s hybrids prae- and posttrematic. 
