Landacre, Taste Buds of Ameiurus. 47 



carry gustatory fibers in Ameiurus and do not in less specialized 

 types are looked upon as routes through which these fibers reach 

 the surface and explain to some extent the discontinuous method 

 of spreading. Finally, the disappearance of gustatory fibers in 

 terrestrial vertebrates from the rami of the V and VII nerves 

 which bore such fibers in aquatic forms may be explained as a 

 process of retrograde degeneration. 



This hypothesis seems to be in accord with known facts and 

 certainly does away with the difficulty of deriving ectodermic 

 from endodermic buds. Spreading of buds from endoderm 

 into ectoderm in the strict sense of the word does not occur in 

 Ameiurus or in any other type so far as the writer is aware. 

 Buds appear in the ectoderm in detached groups. There is 

 a possibility that buds in ectodermic territory may actually 

 spread into endodermic territory, as was mentioned above, in 

 the case of the posterior palatine group. This, however, is 

 probably peculiar to Ameiurus and has no bearing whatever on 

 the question as to where taste buds first appeared phylogeneti- 

 cally. In regard to this problem, the evidence seems to be in 

 favor of Johnston's hypothesis ('05, '06) that buds in primitive 

 forms appear first in endodermic territory, since taste buds are 

 always supplied by communis fibers which are visceral in their 

 relationship as far as their central nuclei are concerned. The 

 hypothesis of Cole ('00, p. 320) that taste buds arose first 

 in the ectoderm and spread into the endoderm seems to be nega- 

 tived by the visceral character of the communis system. Nei- 

 ther the hypothesis of Cole nor Johnston seems to the writer to 

 be tenable, if by spreading is meant continuous spreading; for 

 this method does not occur in Ameiurus, and, as mentioned 

 above, probably not in other types. A more fundamental ques- 

 tion, and one whose solution would include to a large extent that 

 of the place of first appearance, is involved in the source of the 

 specialized portions of the communis system. Have specialized 

 communis or gustatory fibers innervating taste and terminal 

 buds arisen simply through the differentiation of unspecialized 

 communis fibers ? If they have, we should expect taste buds 

 to arise first in the endoderm, as Johnston suggests. 



However, before any definite conclusion is reached we must 

 know the fate of that portion of the geniculate ganglion which 

 is supposed to be derived from the epibranchial placode. It 



