THE CRANIAL GANGLIA IN AMEIURUS 319 



cutaneous fibres in the Vllth in Petromyzon, that the crest is 

 at first continuous but apparently not so later, and that when the 

 Vllth and IXth contain general cutaneous fibres they also contain 

 neural crest cells seem to the writer to minimize the discrepancy 

 between Kolzoff's and Johnston's work, since these cells may enter 

 into the Vllth and IXth in Petromyzon. The matter is compli- 

 cated by the fact that neural crest cells of the Vllth lie between 

 the anterior portion of the auditory vesicle and the neural tube 

 and come into contact with the vesicle at or near the place where 

 the cells of the auditory ganglion are proliferated from the vesicle 

 so that the relations are confused and it is difficult to be certain of 

 the exact conditions. Leaving out of consideration the VHIth 

 ganglion, we can infer that the general cutaneous ganglia come 

 exclusively from the neural crest, while the acustico-lateralis 

 and visceral ganglia come in part from the dorso-lateral and epi- 

 branchial placodes respectively but may contain neural crest 

 cells in some cases. 



Without anticipating the conclusions drawn from a study of 

 Ameiurus, it may be well to call attention to two facts: first, 

 the acustico-lateralis system of nerves and ganglia is usually 

 treated as a special cutaneous system on account of the fact that 

 the tuberculum acusticum which is the acustico-lateralis center in 

 the medulla oblongata is a specialized portion of the general cutan- 

 eous center of the spinal cord extending into the medulla oblon- 

 gata. The close relationship of the general cutaneous and acustico- 

 lateralis systems is thus based on good anatomical evidence. Sec- 

 ond, the communis or visceral system is really double in character; 

 it consists of a general visceral portion which supplies general 

 mucous surfaces, and it also contains a special visceral or gustatory 

 portion whose fibres end peripherally in taste buds, so that the 

 presence of neural crest cells in the acustico-lateralis and visceral 

 ganglia might be explained in the first case on the basis of the close 

 relationship between the general cutaneous and the acustico- 

 lateralis systems of nerves and ganglia and in the second case on 

 the basis of the double composition of the communis or visceral 

 system. 



The determination of the relation of neural crest cells to those 



