Landacre, Taste Buds of Ameiuriis. 19 



the posterior limit in U is 174. In the cutaneous group the cor- 

 responding limits in N and U are 36 and 68. This slower rate 

 of progression, accompanied as it is by the later appearance of 

 the cutaneous buds, probably indicates the phylogenetic relation 

 of these two groups to each other. The oral group would be 

 functionally important regardless of the condition of the eye, 

 while the appearance of the cutaneous buds is probably associated 

 with the reduction of the relative functional importance of the 

 eye in seeking food, which is so characteristic of Ameiurus. The 

 spreading of buds from the oral areas to the cutaneous areas does 

 not involve a very great change, since the two areas are really 

 continuous on the lips and both lie in ectoderm and both are sup- 

 plied by communis fibers from the geniculate ganglion of the 

 seventh nerve. The simultaneous appearance of buds in the oral 

 and pharyngeal areas is, however, much more striking, since one 

 lies in ectoderm and the other in endoderm. This difference 

 might be minimized by lessening the radical distinction which is 

 usually made between endodermic and ectodermic areas, since 

 endoderm is always derived from ectoderm, if it were not for the 

 fact that buds lying in ectodermic areas are supplied by com- 

 munis nerves. Johnston's suggestion that buds spread from 

 endodermic into ectodermic territories, if found to be true in more 

 generalized types, would lessen the difficulty of explaining this 

 curious condition. 



Since taste buds do not spread from endoderm into ectoderm 

 in Ameiurus, some other explanation of their appearance there 

 must be sought which will explain the conditions here, as well as 

 in other types. In the following sections an analysis of the vari- 

 ous subdivisions of the three principal groups mentioned has 

 been made to ascertain if possible what factor has determined 

 the time and place of appearance of taste buds and in particular 

 to see if the distribution was correlated with or controlled by the 

 nerve supply. 



In this analysis four things have been kept in mind: (i) To 

 determine the time of first appearance of taste buds situated in 

 different areas but innervated by fibers from the same nerve, i. e., 

 to see if buds not parts of the same functional unit but having 

 a common innervation appeared at the same time. (2) To deter- 

 mine if buds that are a part of the same functional unit but have 

 their fibers from different nerves appear at the same time. If this 



