6o "Journal of Comparative Neurology and Psychology 



buds spread along the course of any given nerve from the distal 

 toward the proximal areas innervated. As in the case of the 

 oral and cutaneous groups, the smaller subdivisions in which 

 buds appear, can be isolated from each other by their nerve sup- 

 ply as well as by the fact that they are not continuous, struc- 

 turally and that, in point of time, they do not appear simultane- 

 ously. As far as the question of the origin of ectodermic buds 

 is concerned, it is of special interest to note that in the pharyn- 

 geal group no buds spread from endodermic to ectodermic ter- 

 ritory. In fact, there is some evidence that the reverse process 

 takes place in the spreading of buds from the posterior mandib- 

 ular, hyoid and suspensorial groups to the anterior portions of 

 the inner surface of the operculum. The evidence, however, 

 is not conclusive, since we do not know the exact limit of the 

 pharynx in vertebrates. 



In Menidia (Herrick '99) communis fibers run from the 

 ninth nerve into the ramus lat. acces. and probably taste buds 

 are supplied by these fibers in that type. Even this, however, 

 does not involve an actual spreading of buds from endoderm 

 into ectoderm, since if we may draw any conclusion from 

 Ameiurus they probably would be found to appear in discontinu- 

 ous groups. 



If we are to consider the pharyngeal group as the older phylo- 

 genetically, based on the fact that its buds are in endodermic 

 territory and innervated by visceral nerves segmentally arranged, 

 we have a very striking difference in the extent and variety of 

 the areas innervated by the nerves supplying this group as com- 

 pared with the areas innervated by the communis fibers from 

 the seventh nerve. We should expect to find the group which 

 is phylogenetically older to be more stable and to adapt itself 

 to new conditions less easily. All the evidence from Ameiurus 

 goes to show that the gustatory fibers arising from the genicu- 

 late ganglion are more variable, that is, occupy a greater num- 

 ber of nerves and innervate a greater variety of areas, than those 

 of the ninth and tenth nerves. The exceedingly specialized con- 

 dition in Ameiurus must have been derived from a simpler con- 

 dition in which there were fewer areas containing taste buds, 

 fewer nerves carrying gustatory fibers and fewer fibers in any 

 given nerve than were found in less specialized types or in 

 Ameiurus formerly. 



