MORPHOLOGICAL STUDIES. 
197 
their development according to his ideas, as opposed to the 
facts I have here described for Elasmobranchii and Birds. 
The conviction was very early in the research forced upon me 
that the development of spinal and cranial ganglia in all 
Vertebrates must take place after one type, and any differ- 
ences found in different groups must be referable to variations 
or changes rung on that type. And as an example, the inves- 
tigation of the development of cranial ganglia in the Anurous 
Amphibians was one I could not leave unnoticed on account 
of Spencer’s notes on the matter (No. 59). All the more, 
as in my paper on the branchial sense organs (No. 6) I 
felt obliged, after the examination of some of Spencer’s pre- 
parations, and of a few I made myself, to support his conclu- 
sions. We were then both in error on one point — of that I 
am now quite sure — and that is in reference to the deeper 
layer of epiblast above the level of the lateral sense-organ 
thickening, and which connects the latter in early stages with 
the neural plate. We both believed it gave origin to the 
trunk of the nerve. This is not so. That layer is indifferent 
except at two points corresponding exactly to the two points 
at which the ganglionic form elements arise in Elasmobranchs. 
In fact, as a preliminary note I take the opportunity of saying 
that the cranial ganglia of the Frog develop in exactly the 
same way as those of Elasmobranchii. Among other forms 
examined the Lizard is one of the most favorable for such in- 
vestigations. It also agrees essentially in the mode of develop- 
ment of cranial and spinal ganglia with Elasmobranchii. 
The Newt has been mainly studied by Bedot (No. 9), and 
Misses Johnson and Sheldon (No. 38). 
In both of these works I shall have occasion to underline a 
number of mistakes and false interpretations; here I will only 
remark that I am somewhat surprised that none of these in- 
vestigators have seen the epi'blastic origin of the spinal ganglia 
in this animal. I know no animal in which such origin is 
easier to identify. The criticisms with which the two latter 
authors have seen fit to honour my work may also be here left 
unnoticed. The only one whose justification I will acknow- 
VOL. XXIX, rART 2. NEW SER. 
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