466 



L. S. STONE 



Fig. 49 Camera drawing, showing absence of hyomandibular group of sense 

 organs after removal of an area of ectoderm shown in figure 50. X 10. 



Fig. 50 Camera drawing, showing by dotted line an area of ectoderm removed 

 at stage 26 in which was included the primordium of the hyomandibular group of 

 sense organs as well as epibranchial placode of VII and supra-orbital primordium. 

 X 10. 



Fig. 51 Camera drawing, showing by dotted line an area of excised ectoderm 

 in which was included the primordium of the ventral hyomandibular group of 

 sense organs and part of the primordium of mandibular group. X 10. 



Fig. 52 Camera drawing, showing by dotted line position of implanted blue 

 ectoderm a few days after operation in same individual shown in figure 51. The 

 balancer is absent on operated side. X 10. 



Fig. 53 Camera drawing twenty-one days later of the ventral side of embryo 

 shown in figure 51. On the operated side there is only a small portion of the man- 

 dibular group of sense organs, while the ventral hyomandibular group is entirely 

 absent. X 10. 



