CRANIAL GANGLIA OF AMBLYSTOMA 



443 



numerous mitotic figures showing a rapid development of placodal 

 cells (fig. 27). It is difficult to mark off the upper portion of this 

 placode because of its proximity to the ventral border of the loose 

 cells of the lateral-Une ganglion above. The primordium of the 



27 



29 



Fig. 27 Frontal section, showing epibranchial placode of VII in stage 33 

 proliferating a large mass of cells. X 37. 



Fig. 28 Frontal section, showing in stage 33 lateral-line ganglion and placode 

 of VII, rounded epibranchial placode of I^ on left side and epibranchial placode 

 of X on right anterior to X lateral-line placode in process of forming ganglion. 

 X 37. 



Fig. 29 Frontal section, showing at stage 33 lateral-line placode of IX pos- 

 terior to auditory capsule. X 37. 



Fig. 30 Frontal section, showing at stage 35 crest cells surrounding meso- 

 derm of mandibular, hyoid, first and second branchial arches and also increase 

 in number of crest cells on median side of hyoid arch. X 37. 



ventral hyomandibular line of sense organs in the lower portion 

 of the hyomandibular cleft is somewhat elongated and deeper 

 than in stage 30. The epibranchial placode of IX (fig. 28) is 

 giving off a rounded mass of cells just above and slightly posterior 



