464 



L. S. STONE 



It seems quite evident from these results that the ectodermal 

 adhesion of the early gasserian ganglion is in the nature of a small 

 placode which contributes cells to the formation of that ganglion. 



3. Removal of preauditory placode and the supra-orhital pri- 

 mordium. In this type of operation the rectangular area of 



Fig. 46 Camera drawing showing area of ectoderm excised in removing pre- 

 auditory placode and supra-orbital primordium. Outlined by means of dotted 

 lines and the middorsal line. X 10. 



Fig. 47 Camera drawing, showing absence of the supra-orbital group of sense 

 organs after removal of an area of ectoderm as shown in figure 46. X 10. 



Fig. 48 Camera drawing, showing only three or four supra-orbital lateral 

 line sense organs when not all of the early preauditory placode is removed during 

 stage 21. The lightly pigmented area of transplant of indifferent ectoderm at 

 time animal was killed is shown by dotted line. X 10. 



ectoderm excised is outlined in figure 46. Indifferent ectoderm 

 from the ventral side of another animal of the same age which 

 had been previously stained with Nile-blue sulphate was grafted 

 into the wound. This operation was confined to stages under 

 stage 25. 



