38 'Journal of Comparative Neurology and Psychology. 



Of the 14 buds found in the 20J mm. embryo, one is found 

 between the third and fourth main lateral line organ, one on the 

 skin over the fourth organ, eight are found between the fourth 

 and fifth organ, and four between the fifth and sixth organ. 



This body group shows a well defined progression posteriorly 

 as measured by the lateral line organs, moving back from the 

 area between the third and fourth to that between the fourth 

 and fifth and later to that between the fifth and sixth. The 

 nerves supplying these buds run out from the ramus lat. acces. 

 through spinal rami, which are, of course, arranged segmentally, 

 but no further evidence of a segmental arrangement can be 

 detected than that noted in the table, and I am inclined, of course, 

 from a study of the anterior oral and cutaneous buds to con- 

 sider the segmental arrangement of buds here to be purely sec- 

 ondary; that is, they are segmental simply because they are 

 innervated by nerves that are segmental on account of having used 

 segmental spinal nerves as a means of reaching the surface. 



The question as to whether these buds spread out from the 

 gills or spread back from the post-orbital group will be only 

 mentioned here, and will be discussed more fully with the pha- 

 ryngeal buds. Their continuity in time of appearance is cer- 

 tainly with the post-orbital group, and their innervation is from 

 the seventh nerve, along with the post-orbital group and buds 

 lying farther forward about the anterior portions of the head. 

 The only two ways in which continuity in distribution could be 

 established with the pharyngeal group, would be for the pharyn- 

 geal buds to spread out from the under side of the operculum 

 to the body or else from the bases of the gills down to the ven- 

 tral surface of the isthmus and thus to the body. It will be seen 

 later that neither of these movements takes place. We must con- 

 clude from the time of the appearance, the continuity in distri- 

 bution and the innervation that they are related to other buds 

 on the head and operculum and are part of the general spread- 

 ing of buds from the anterior to the posterior portions of the body 

 surface. They represent the posterior extension of a function- 

 ally more or less homogeneous group of buds enabling Ameiurus 

 to ascertain the location of sapid substances when the stimulus 

 reaches portions of the body other than the mouth and the 

 pharynx. 



The spreading of buds from the place of appearance on the 



