MORPHOLOGICAL STUDIES. 
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motor nerves is brought about rather by a chain of ganglionic 
cells. 
I, b . The Cranial Ganglia in Elasmobranchii. 
Compared with the development of the cranial ganglia that 
of the spinal ganglia previously described is simplicity itself. 
For just as the head of Vertebrates presents, when compared 
with the trunk, a complexity of problems, the solution of which, 
in the opinion of morphologists like Huxley, Dohrn, Froriep, 
and others, will take years of careful work, so also the cranial 
ganglia present a number of problems, towards the solution 
of which I only can hope to go a little way in the following 
pages. 
While there can be no sort of doubt that the spinal ganglia 
are strictly segmental in their origin — indeed, that such is the 
case is easily demonstrable — the reduction of the cranial 
ganglia to segmental order is a task of great difficulty. It 
has been objected by Dohrn and others that the setting up of 
tables showing the segmental nature of the head nerves is a 
proceeding which is to be deprecated, and that the true 
problem is the reduction of the components of the head to 
simpler Aunelidan structures. To which one may reply that, 
according to Dohrn, such Annelid ancestors were segmented 
animals, and no matter how complex the Vertebrate head may 
now be, it is at its basis composed of a number of Annelid 
metameres, and the unravelling and ordering of the existing 
complex, as far as it is possible, is the real task of the 
morphologist. 
I shall not at the moment attempt to discuss again the 
claims of the various cranial nerves to “segmental rank/’ a 
proceeding which, to my mind, is entirely justifiable, for it has 
its meaning in the sorting of the cranial nerves for morpho- 
logical (and physiological) considerations. Still, in the follow- 
ing account of the very first signs of the cranial ganglia, I 
must insist on such points of development as support, for 
instance, the comparison of the auditory and olfactory ganglia 
and sense organs with those of, for example, such a typical 
