THE CRANIAL GANGLIA IN AMEIURUS 367 



fluent and always appear in order from anterior to posterior. The 

 taste buds show one other peculiarity in their order of appear- 

 ance. They appear, generally, at the peripheral distribution of 

 the nerves innervating them anterior to the ear, and in the reverse 

 order posterior to the ear. It is evident from these facts that 

 they are in no way, in Ameiurus, closely related in place of origin to 

 the epibranchial placodes. The epibranchial placodes, so far as 

 any evidence secured from their ontogeny indicates, are to be 

 looked upon as ganglion forming structures. The epibranchial 

 placodes bear no resemblance to either single taste buds or groups 

 of taste buds. These buds spread in the case of the oral and super- 

 ficial head buds from the point of origin toward, and not away 

 from the point of origin of the placodes. 



An additional fact of significance is the time intervening between 

 the detachment of a given placode and the appearance of the first 

 taste buds innervated by fibres derived from the ganglion formed 

 by the placode. In the IXth nerve, the placode which forms t lit' 

 special visceral ganglion of that nerve becomes detached in a 

 93-hour embryo (A. melas), but the first taste buds on the 

 pharynx, and, in fact, on any part of embryo, appear in a 113- 

 hour embryo ; a length of time sufficient to suggest tht the appear- 

 ance of the taste buds is associated with the appearance of the 

 nerve trunk, rather than with the proximity of the taste buds to 

 the placode, since the IXth nerve has a fibrillated root and trunk 

 which extends into the first gill arch in an embryo on 113 hours. 



The process of growth by which the various components of 

 the peripheral nerves find their appropriate sense organs furnishes 

 one of the most puzzling problems in embryology. This is especi- 

 ally true of the gustatory nerves and taste buds, and in a measure 

 is true of the lateralis system of nerves and sense organs. The 

 solution does not seem to lie in deriving both nerves and sense 

 organs from a common primordium, as can be done in the case of 

 the olfactory nerve and optic nerve. The distance between the 

 point of origin of taste buds supplied by the Vllth nerve and the 

 point of origin of the ganglion of the Vllth nerve precludes such 

 an explanation. The suggestion offered above that there is some 

 coordination in the growth of the peripheral fibres and the appear- 



