462 L. S. STONE 



study of the records of the growth of the transplanted blue 

 ectoderm of this individual shows that not all of the ectoderm 

 concerned in the formation of the ophthalmic ganglion was elim- 

 inated from the ectoderm in the region anterodorsal to the 

 optic vesicle. 



A control operation was made on several specimens in which 

 the ectoderm was excised as in the usual operative procedure and 

 replaced and allowed to heal into its normal position. When 

 these specimens were sectioned they showed perfectly normal 

 ophthalmic ganglia, indicating that if there had been any dis- 

 turbance of the crest cells in the trigeminal region during the 

 operation it did not, in itself, affect the formation of the ganglion. 



A large number of individuals in which the excised area con- 

 taining the preauditory placode and supra-orbital primordium 

 was removed along with some of the ectoderm above the optic 

 vesicle, show a similar displacement of the ophthalmic ganglion. 

 Among these cases where the embryos were preserved within a 

 few days after the operation ganglionic masses of cells lie close 

 to the ectoderm. Their posterior ends become attenuated and 

 no connection to the brain is discernible. The older individuals 

 which were sectioned show cutaneous fibers issuing from the 

 ganglionic mass comparable in their distribution to the fibers 

 from the ophthalmicus profundus V nerve as in the case already 

 cited (fig. 45 b). 



It seems quite evident from the above results obtained that the 

 formation of the ophthalmic ganghon is largely if not entirely 

 dependent upon the placode in the ectoderm above the optic 

 vesicle. 



2. Removal of gasserian placode. A rather extensive rectangu- 

 lar piece of ectoderm was removed, including all the ectoderm 

 around the dorsoposterior quadrant of the eye. An incision was 

 made beginning at a point on the hyoid arch at a level with about 

 the middle of the eye and passing dorsally some distance in front 

 of the auditory placode to a level about the middle of the latter. 

 The incision was then extended anteriorly parallel with thii^ ^V 

 dorsal line to a point above the middle of the eye. From this 

 point it was carried ventrally to a little above the middle of the 



