170 ROSS G. HARRISON. 



EXPLANATION OF PLATE I. 



Figure i. Profile view of an embryo of Amblysloma punclatum, stage 21. The 

 various flaps of ectoderm used in the transplantations are indicated by ovals. A, 

 includes the mandibular, hyoid and anterior part of the branchial region; BR, 

 branchial region; C, ventroanterior part of head region; C', head region; CD. 

 cardiac region; Fl, flank; PN, pronephric and limb region. X 10. 



Figure 2. Replacement of branchial ectoderm by ectoderm from the flank 

 (Exp. E. Br. E. 21) resulting in complete suppression of gills on the right side; 

 ventral view of larva eighteen days after operation. X 10. 



Figure 3. 'Larva, with gills almost suppressed through failure to regenerate after 

 removal of branchial ectoderm (Exp. E. Br. M 15-); specimen preserved thirty- 

 six days after operation. X 10. 



Figure 4. Larva with abnormal gills on the right side due to inversion of the 

 branchial ectoderm and mesoderm (Exp. Br 35), specimen preserved fifteen days 

 after operation. X 10. 



Figure 5. Individual showing normal gills developed from double quantity of 

 mesoderm (Exp. S. Br. 17); specimen preserved ten days after operation. X 10. 



Figure 6. Individual in which branchial ectoderm (Fig. i, BR) had been 

 transplanted to a position just anterior to gill region (Fig. i, A) (Exp. Br. A 2); 

 two supernumerary gills (H and M) developed; the dotted line indicates the boun- 

 dary of the transplanted ectoderm; sketch made ten days after operation. X 10. 



