PLATE 3 



EXPLANATION OF FIGURES 



16 The pigmentary system of a 10-mm. (total length) albino frog tadpole, 'stand- 

 ard' environment. Dropped into Helly's fluid 22 days after the operative stage. 

 Liver diet. The epidermal melanophores have not yet formed. X226. 



17 The pigmentary system of a 14.5-mm. (total length) normal frog tadpole, 

 'standard' environment. Fixed by dropping into Helly's fluid 47 days after the 

 operative stage. Liver diet. X226. 



18 The pigmentary system of a 14.5-mm. (total length) albino frog tadpole, 

 'standard' environment. Fixed by dropping into Helly's fluid 47 days after the 

 operative stage. Liver diet. X226. 



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