Landacre, Taste Buds of Ameiurus. 6l 



17. GENERAL SUMMARY. 



1. Taste buds appear simultaneously in the extreme ante- 

 rior portion of the oral cavity (ectoderm) and on the endoderm 

 of the first three gill arches. 



2. Buds always spread posteriorly from these places of ori- 

 gin by discontinuous groups. Those of the pharynx spread 

 back into the oesophagus and are continuous with the buds on 

 the last gill arch. Those of the anterior oral cavity spread back 

 in the mouth by discontinuous groups until they reach the area 

 occupied by the pharyngeal buds and also spread back on the 

 outer surface of the body by discontinuous groups until they 

 reach the posterior portions of the body. 



3. No buds spread from the pharyngeal group to the outer 

 surface of the body at least as late as the 20| mm. embryo when 

 all of the main groups on the head and body are present. 



4. The first buds to appear on the outer surface of the body 

 are continuous with those just inside the lips. All the remaining 

 buds appear in discontinuous groups determined partly by the 

 distribution of the rami of the V and VII nerves but not entirely, 

 since these groups may be innervated by one, two, or as many as 

 five rami, or two closely related rami may innervate different 

 groups, so that some factor other than the mere anatomical arrange- 

 ment of nerve rami is necessary to explain the uniform anterior- 

 posterior appearance of discontinuous groups. 



5. There are six well defined groups of buds on the outer sur- 

 face of the- body isolated in position by the fact that there are 

 areas devoid of buds between them at the time of their appearance, 

 and separated in time of appearance by periods ranging from 

 seven to more than 100 hours for groups that later become con- 

 tinuous. There are two well defined groups of buds in the 

 anterior oral cavity distinct from the dorsal and ventral lip buds. 



6. The pharyngeal buds are segmentally arranged and appear 

 on the gills in order from anterior to posterior. The spreading 

 from anterior to posterior is characteristic of oesophageal buds 

 and they are continuous with buds on the last gill arch. 



7. In the oral and cutaneous groups of buds and to a certain 

 extent in the pharyngeal, the buds situated on the peripheral dis- 

 tribution of a nerve appear before those on the proximal distri- 

 bution. This is reversed in the case of buds situated on areas 



