THE CRANIAL GANGLIA IN AMEIURFS 371 



derived from the lateral mass are hard to distinguish from the 

 surrounding mesectoderm. One can go no farther than to say 

 that there is no well defined group of lateral mass cells entering 

 into the lateralis IXth ganglion. The condition found in most of 

 my series during the early proliferation of cells from the auditory 

 vesicle before the definitive lateralis ganglion is formed, is illus- 

 trated in fig. 63. The lateralis IXth after it assumes a definite 

 form is carried posteriorly by the backward growth of the audi- 

 tory vesicle until it comes into the region of the slightly denser 

 mass of mesectoderm, which at the time the lateralis IXth can 

 first be detected is about seven sections posterior to the vesicle. 

 This loose mass of cells, as mentioned above, is present in one of my 

 series (A. nebulosus, Stage VII, figs. 40, 41, G), but in only one is 

 it at all definite or does it present the appearance of an early stage 

 of a ganglion. I take it to be the mass of cells which other authors 

 have described as neural crest cells that enter into the IXth gan- 

 glion. , 



The early appearance of the definitive lateralis IXth ganglion 

 is somewhat variable. It may not appear on both sides of the 

 same embryo at the same time, and may vary in position, lying 

 either on the ventro-mesial (fig. 61) or on the ventro-lateral side 

 (fig. 62) of the posterior portion of the auditory vesicle. The 

 definitive ganglionic mass may appear as a few loosely joined 

 cells, some of which are still not entirely detached from the wall 

 of the vesicle. 



As in the case of the auditory ganglion, one can be quite sure 

 that the bulk of the lateralis IXth ganglion is derived from the 

 auditory vesicle. In the early stage of the vesicle there is no 

 ganglionic mass in the position later occupied by the lateralis 

 IXth, and the walls of the posterior end of the vesicle are clean 

 cut and regular. Somewhat later the posterior wall becomes 

 several cells thick, mitotic figures are numerous and a mass of 

 cells is found attached to the ventro-mesial or ventro-lateral 

 portion of the vesicle. No definite boundary can be determined for 

 the forming ganglion, and cells are found in all positions between 

 the wall of the vesicle and the body of the ganglion (fig. 63). 



