20 'Journal of Comparative Neurology and Psychology. 



proves to be the case, the functional unit is the prime factor in 

 determining the time of the appearance and direction of spread- 

 ing of groups. Neither of these questions can be answered, of 

 course, except in groups of buds, the smaller subdivisions of which 

 have a single innervation. (3) To determine, if possible, whether 

 buds appear first on the peripheral or proximal distribution of 

 a nerve. This ought to throw some light on the manner in which 

 gustatory fibers reach the areas they innervate. (4) To deter- 

 mine if buds appear in any definite order on structures segmentally 

 arranged, such as those in the gill region. 



The description of the relations of the various areas to the 

 nerve supply is based, as mentioned before, on the account of 

 the communis system of Ameiurus by C. J. Herrick ('01), mainly, 

 although not entirely for the pharyngeal regions. The reader is 

 referred to that paper for a fuller description of these nerves; only 

 so much of it is incorporated here as is deemed necessary to make 

 the correlation clear. 



The term "functional unit," as used in the following descrip- 

 tion, is applied to groups of buds, discontinuous at the time of their 

 appearance, which from their position on the body would seem 

 to function as units, that is, be stimulated in unison. They are 

 characterized, first, by having areas between them and other 

 groups devoid of buds at the time of their appearance, although 

 they may become continuous later with these groups; and, second, 

 by differences in time of appearance, this difference varying from 

 a few hours up to one hundred or more for adjoining groups 

 which may later become continuous. The units are composed of 

 smaller subdivisions closely related to the number of nerves sup- 

 plying the unit. These show the same manner of spreading as 

 the larger unit of which they are part. 



4. THE DORSAL LIP AND MAXILLARY BARBLET GROUP. 



This group includes buds lying on the upper lip both inside the 

 lip and on the outside, buds lying on the maxillary barblet and 

 on the dorsal breathing valve. The first buds to appear in this 

 group are situated on the lateral portion of the upper lips, the 

 dorsal breathing valve and the region of the premaxillary teeth 

 and on the base of the maxillary barblet. Buds appear on the 

 base of the maxillary barblet of K' (118 hours). As mentioned 

 before, these may be really internal lip buds and not on the outer 



