CRANIAL GANGLIA OF AMBLYSTOMA 479 



region of the mesoderm of the hyoid and the first and second 

 branchial arches a distinct lack of crest cells on the operated side, 

 while on the normal side they are abundant and still surround 

 the mesoderm of the arches. 



Case 3. A similar specimen was killed nine days after opera- 

 tion, when it had reached about stage 37. The external gills at 

 this stage have become prominent finger-like processes, but have 

 not "developed branches. A frontal section of this specimen 

 (fig. 70), although obUquely cut, shows to even more advantage 

 the comparison of the two sides, for the level of the operated 

 side is lower where there would be normally an abundance of 

 procartilage-forming cells. There are but three crest cells in the 

 region of the third branchial arch, while the others lack cells of 

 this kind altogether. This is the condition in sections above this 

 level. The crest cells in the hyoid region are also noticeably less 

 in amount than on the left side. At a lower level (fig. 71) the 

 difference is more striking, for the hyoid, the first, and part of 

 the second branchial regions have very few cartilage-forming 

 cells compared with the abundance on the normal side. Loose 

 connective tissue in the external gills on the operated side is also 

 subnormal in amount. 



Case 4. This specimen was killed fourteen days after the 

 operation, when it had reached about stage 39. The gills on the 

 operated side are smaller than on the normal side and their con- 

 nective-tissue cells are less numerous. Compared with the nor- 

 mal side, there are only a few procartilage cells in the third and 

 fourth branchial arches (5g. 72). When followed farther ven- 

 trally (fig. 73), the few loose cells on the right side increase but 

 slightly in number and always remain much more loose in ar- 

 rangement as they approach in the midline the normal compact 

 procartilage. The procartilage in the hyoid region is also much 

 less in amount. 



Case 5. This specimen was killed seventeen days after opera- 

 tion and also shows a decided diminution in the size of the gills 

 on the operated side. A frontal section shows well-formed 

 branchial cartilages on the left, w^hile on the right a few cells 

 form a small cartilage only in the third gill arch. When followed 



