336 F. L. LANDACRE 



tion of the literature throws little light on the question. Dohrn 

 ('90), however, taking this matter up specifically states that the 

 neural crest is present at first in the auditory region but that it 

 disappears. It was hoped that Ameiurus would throw light on 

 the question, but the fact that there is no specific neural crest in 

 Ameiurus renders my conclusions somewhat unsatisfactory in 

 this matter. Since, however, there is no remnant of the lateral 

 mass left in the auditory region after the vesicle forms, we may con- 

 clude that whatever the relation of the neural crest of other types 

 to the lateral mass of Ameiurus the position taken by Dohrn is 

 strongly supported by the evidence from this type and I find 

 myself in agreement with Johnston ('06) when he states that the 

 neural crest is absent in the auditory region. This statement 

 will not hold for the region immediately anterior to the auditory 

 vesicle, as was shown in describing the differentiation of the pre- 

 auditory lateral mass. The lateral mass there furnishes the two 

 lateralis ganglia of the Vllth nerve. 



The exact mode of origin of the VHIth ganglion is complicated 

 by the fact that, while it seems to come almost entirely from the 

 anterior end of the auditory vesicle, it develops in such close 

 proximity to the preauditory lateral mass which gives rise to the 

 lateralis Vllth ganglia and is so closely fused with the ventro- 

 mesial ganglion of these two ganglia that it is impossible to be cer- 

 tain of its exact composition. In the stage in which the auditory 

 vesicle is first recognizable by the radial arrangement of its cells 

 there is no mass of cells occupying the position of the future audi- 

 tory ganglion; this, when it appears as a definitive mass, is situated 

 as a cap of cells adhering closely to the ventral and ventro- 

 mesial portion of the anterior portion of the vesicle and extending 

 slightly beyond the anterior end. Here it comes into contact with 

 the irregular mass of cells which differentiates later into the later- 

 alis ganglia of the Vllth nerve. At this stage before the appear- 

 ance of the auditory ganglion and up to the time the preauditory 

 placode separates from the vesicle the anterior walls of the vesicle 

 are well defined and there is no evidence that cells are being pro- 

 liferated from it. However, shortly after the separation of the 

 preauditory placode from the vesicle the walls of the anterior 



