320 F. L. LANDACRE 



cells derived from the dorso-lateral and epibranchial placodes was 

 one of the chief objects in taking up the study of Ameiurus. Un- 

 expected difficulties were met, owing to the fact that Ameiurus 

 has no well defined neural crest in the head such as is found in 

 other types, so that my conclusions are based on the assumption 

 that there are in Ameiurus cells which correspond to the neural 

 crest of other types. Aside from this peculiarity, it has proven to 

 be an exceptionally favorable type. The epibranchial placodes 

 are large and easily followed and the epibranchial ganglion of the 

 IXth nerve seems to be a pure placodal ganglion, a fact which 

 enables us to come to a definite conclusion in regard to the rela- 

 tion of the neural crest cells to those derived from the placode. It 

 seems to be necessary to determine this point definitely before we 

 can come to any satisfactory conclusion as to the relation of the 

 spinal and cerebral ganglia to each other. The acustico-lateralis 

 and gustatory nerves are peculiar to the head but the general 

 visceral and the general cutaneous are not, being found in the 

 trunk. The problem of the relation of spinal and cerebral nerves 

 becomes largely a question as to how the general visceral and 

 general cutaneous nerves are related in origin to the special vis- 

 ceral and special cutaneous nerves in the head. Aside from the 

 fact that it was necessary to choose some type in which the nerve 

 components are known, the chief reason for taking Ameiurus lies 

 in the enormous size of the gustatory system of sense organs and 

 nerves. The taste buds are distributed over practically the whole 

 body surface as well as in the mouth* pharynx and oesophagus, and 

 gustatory fibres a/e found in ten out of twelve of the chief nerves 

 arising from the trigemino- facial ganglia. A type with such an 

 enormously hypertrophied gustatory system seemed likely to 

 furnish a good basis for determining the exact mode of origin of 

 the special visceral ganglia and nerves. 



A summary of the cranial ganglia of Ameiurus as given by 

 Herrick ('01) is shown in the following diagram: 



