184 J. B. JOHNSTON, 
hypothesis which I stated in my previous paper: “That all sensory 
structures of ectodermal origin are supplied by components of the 
V (including V components running in other nerves), VIII and 
lateral line nerves, and that all fibres supplying such structures have 
their central endings in the nucleus funiculi, tuberculum acusticum, 
or the cerebellum ..... On the other hand, all sensory structures 
of entodermal origin are supplied by VII, IX and X components 
and all fibres supplying such structures find their central endings in 
the lobus vagi.” This hypothesis had its origin wholly in the results 
of my work on the central system (see ‘98b, p. 594). As I worked 
on the structure of the medulla and the central endings of the cranial 
nerves it occurred to me that it was as legitimate to proceed from 
their central as from their peripheral distribution in attempting to 
discover their functions and homologies. Wide differences in the 
central relations of two components in the cranial nerves constitute 
good ground for the expectation that they will be found to differ in 
their peripheral distribution and their functions. It has been known 
since the work of STRONG that the fasciculus communis components 
in the VII-IX-X nerve group are at least chiefly engaged with 
sensory impulses which arise in the viscera and commonly result in 
involuntary movements. The V-VIII-lateral line nerve group in- 
nervate cutaneous sense organs and carry stimuli which more often 
lead to sensations and voluntary movements. The functions of the 
communis system are organic, general, or internal; those of the 
cutaneous components are somatic, definite or conscious, and ex- 
ternal, related to environment. In the central relations of these 
components I found fundamental differences amounting to complete 
functional isolation. I therefore concluded that in their distribution 
they would be found as completely isolated. 
In expressing this hypothesis I made an unconscious assumption 
which can not as yet be regarded as beyond doubt, namely that all “‘or- 
ganic” functions are mediated by entoderm or entodermal derivatives. 
In further criticizing the hypothesis it will be necessary to look at 
its physiological and morphological import separately. The only 
facts which seem to be opposed to the hypothesis in either of its 
aspects relate to the innervation of end buds, including taste buds. 
The buds in the mouth and pharynx are undoubtedly in part gust- 
atory and in part serve to test the water with reference to respi- 
ration. Do the buds on the external surface have similar functions ? 
Some attention to the feeding habits of Acipenser leads me to think 
