THE CRANIAL GANGLIA IN AMEIURUS 359 



says (p. 246) in discussing the fate of the preauditory placode 

 (branchial sense organ) that "the further development of the 

 organ consists in the loss of its cavity, in histological differen- 

 tiation, and in the transformation of its ill-defined anterior ex- 

 tremity into two cellular cords which doubtless serve as source 

 for the production of new organs." On the following page in 

 discussing the anterior sensory tract he states thac "during lar- 

 val life one or two sense organs are found in this region and it is 

 extremely probable that they arise from the dorsolateral tract. " 

 In the following paragraph is the statement that "the anterior 

 sensory tract is at the time of hatching very short and just what 

 becomes of it I do not know." This anterior sensory tract is the 

 tract which Wilson derives from the anterior end of the branchial 

 sense organ and which gives rise by its forward extension to two 

 tracts. 



It may be well to call attention to the fact that where Wilson 

 makes unequivocal statements in regard to the relation of the 

 auditorj r vesicle to the preauditory placode, and to the post audi- 

 tory placode in part, we are in essential agreement, i.e., in the 

 origin of the auditory vesicle and the pre- and postauditory 

 placodes from a common primordium, the detachment of these 

 placodes from the vesicle and in the disappearance of the pre- 

 auditory placode. Wilson finds that the preauditory placode 

 disappears, while the postauditory continues to grow back giving 

 rise to the lateral line, but I find that both the pre- and post- 

 auditory placodes finally disappear. With this exception up to 

 this point the two accounts are quite similar. The presence of 

 sensory cells in Wilson's branchial sense organ and their absence 

 in Ameiurus is not a radical difference, especially since the pre- 

 auditory placode in Ameiurus has such a close resemblance to the 

 auditory vesicle. 



As to the point of difference, a careful reading of Wilson's 

 paper fails to show a definite relation between the branchial sense 

 organ and the anterior sensory ridges, and the specific lateral 

 line organs. The disappearance of the branchial sense organ 

 and the anterior sensory tract, and the appearance of specific 



