MORPHOLOGICAL STUDIES. 
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truth in Henseu’s suggestions, though not quite the same 
Hensen thought. 
It is perhaps unkind to remind Professor His that his 
“ Zwischenstrang” was originally believed by him to be con- 
cerned in the formation of the urogenital system. The 
Zwischenstrang was afterwards converted in the basis of a 
theory of the origin of the spinal ganglia. In spite of the 
persistent way in which Professor His, without full and com- 
plete investigation of the matter, holds to this Zwischenstrang 
theory of the proved origin of spinal ganglia, a persistence 
which leads him in his recent work (No. 34, pp. 391 and 416) 
to identify it with what Balfour, Marshall, Sagemehl, and 
others have regarded as the first stages in the formation of the 
ganglia, and to rebaptize the structure, which undoubtedly 
exists (figs. 97, 98, 99, z.), under the name of “ Ganglionstrang,” 1 
I do not see how Professor His can escape the fatal conse- 
quences of the researches I now record. 
I think I have demonstrated, even to Professor His’s satis- 
faction, that the Zwischenstrang is just that part of the epiblast 
which takes no part in the ganglionic formation, and that it 
owes its formation to the cutting out of ganglionic Anlagen 
between it and the neural plate. As the crowning proof that 
the Zwischenstrang is not identical with the neural ridge or the 
1 Professor His (No. 34, p. 417) states that both olfactory and auditory 
organs of Vertebrates take their origin from parts of the “ Zwischenrinne ” 
or “ Ganglienrinne ” which remain open. This is absolutely incorrect. The 
views of the homology of both these organs with the lateral or branchial 
sense organs, which I formerly advocated (Nos. 6, 5, 4), can be still main- 
tained. Prom figures in my former work (No. 6) and figs. 25, 27, 46 of this 
paper, it is obvious to any unprejudiced observer that the auditory organ 
develops ganglionic elements from two sources, just as occurs in a typical 
gill-bearing segment. The same holds for the olfactory organ. I postpone 
for the time the further elucidation of my views of the homology of these 
two sense organs, but only for a time, for I intend shortly to discuss the 
problems they present more fully ; here I will only say that no one has as 
yet urged unanswerable arguments against my views. Personally, I may 
remark, I care nothing about the quondam existence of gill-clefts for ear and 
nose ; the important points to me are those which make the nose and ear parts 
of the system of lateral or branchial sense organs. 
