Landacre, Taste Buds of Ameiurus. 49 



that there is a movement of the buds from the ventral half of the 

 gill arch dorsally toward the roof of the pharynx. The appearance 

 of buds on the roof in series O', where four buds are present, 

 is due to this spreading of the gill buds to the area over the gill 

 arches. Buds appear much earlier on the floor of the pharynx, 

 where they are situated on a prominent ridge exactly in the me- 

 dian line. These mid-ventral buds appear much larger in their 

 immature stages than any other buds in the embryo, but at their 

 later stages are perfectly typical. Their apparently larger size 

 is due to the fact that the ridge itself, which is segmented, may 

 be very easily mistaken for the taste buds. 



This mid-ventral series, situated as it is on a prominent ridge, 

 is well defined in its situation and there is no difficulty in sepa- 

 rating it from adjoining lateral areas except in the later series 

 R, S, T and U, where the buds appear on the fifth arch. Here 

 it is difficult to separate the two series on account of the enlarge- 

 ment of the copula by the appearance of the inferior pharyngeal 

 teeth and also on account of the fact that the cartilages of the 

 fifth arch lie parallel to the copula. 



Buds appear in the oesophagus first in series S, where there 

 are two, and increase to 22 in U. In the oldest series 20J mm. 

 there are about 60. 



Leaving out of consideration for the present the hyoid group 

 and those buds on the floor of the pharynx, the most evident 

 thing about this table is the progression from an anterior to a 

 posterior position of buds on the gills and in the oesophagus. 

 There is here a segmental or branchiomeric order of appear- 

 ance arranged in the following manner. Buds probably ap- 

 pear first on the first gill, then on the second, then on the third, 

 and then on the fourth gill arches, and finally appear in the 

 oesophagus. The dorsal and ventral groups, as will be seen 

 later, correspond quite closely in their segmental arrangement 

 with the gill buds. This order probably represents not only 

 the ontogenetic but the phylogenetic method of appearance as 

 well. The segmental appearance of buds in the pharynx is in 

 sharp contrast with the method by which they appear in the 

 oral and cutaneous groups. 



The apparent exception to the segmental appearance of the 

 buds in serial order in this group is furnished by the hyoid arch 

 and the ventral pharyngeal buds. The hyoid arch lies anterior 



