46 ^Journal of Comparative Neurology and Psychology. 



degeneration of sensory fibers and the loss of ganglion cells. The 

 disappearance of specialized communis fibers in terrestrial ani- 

 mals mio;ht be accounted for on some such basis as the above. 



Fourth, the varying extent of the body covered by taste buds 

 in different types and the varying number of nerve rami through 

 which gustatory fibers from the geniculate ganglion run in dif- 

 ferent types indicate a very great degree of variability in this 

 ganglion. Any variation in the number of sensory fibers must 

 of course be traced to the variability in the ganglion from which 

 they come. As to the variation in the number of taste buds, it 

 seems hardly probable that they could have increased in num- 

 ber by varying fortuitously and later have been connected with 

 gustatory nerves, since this would involve the origin and devel- 

 opment of a definitely constructed sense organ, in types having a 

 peripheral and central nervous system, that would have to exist 

 as such without a function until connected with its appropriate 

 nerve. Whatever may have been the phylogenetic method of 

 origin of specialized communis fibers supplying specialized sense 

 organs, the method in higher types seems to be that the special- 

 ized communis fiber produces its appropriate organ on reaching 

 the surface. 



As to the possibility of variations in ganglia in general, the 

 work of Hardesty ('05), Hatai ('02) and Ranson ('06) is 

 interesting. Ranson, in particular, has shown that the same 

 spinal ganglion may vary by as much as 21 per cent of the total 

 number of cells in the smaller ganglia in white rats of the same 

 age. All three of these authors have called attention to the fact 

 that ganglia always contain a large excess of cells over the num- 

 ber of fibers coming from these ganglia, which would seem to 

 indicate that we have here a structural basis for variation in the 

 number of functional cells and fibers. 



The explanation of the methods of increasing gustatory areas 

 supplied by the V and VII rami mentioned above, may be 

 stated provisionally as follows: The geniculate ganglion varies in 

 the number of gustatory fibers it sends to the surface in various 

 aquatic types and in different ages in the same type, as in Ameiu- 

 rus. Some of these fibers on reaching the surface produce taste 

 buds, whether in the ectoderm or endoderm. The functional 

 needs of the organism determine the direction and manner of 

 spreading, The various rami of the V and VII nerves which 



