1913] Johnson: Pigment Formation in Amphibian Larvae 81 



together, while in the light egg-fed tadpoles, the chromatophores, 

 though perhaps not less numerous are more slender and delicate 

 and very little branched. In very light specimens the pigment 

 is in spots that are scarcely elongated at all (pi. 1, figs. 5-8). 



The form of the chromatophores in the Hyla is somewhat 

 different. The body of the chromatophore is not so long, but the 

 branching processes are longer and finer and in dark individuals 

 form a close network of fine interlacing branches (pi. 1, figs. 3 

 and 4). Between the two extremes in both species are various 

 grades of difference, so that the chromatophores of an unusually 

 dark egg-fed tadpole may not differ greatly from those of a 

 lighter colored liver-fed individual. 



A study of sections shows that the chromatophores of the dark 

 tadpoles are larger because they contain many more of the 

 brown melanin granules. These granules are so numerous that 

 the pigment forms a continuous network in the intercellular 

 spaces, while in the light tadpoles the amount of melanin is so 

 much less that the pigment masses appear as small spots with few 

 or no processes. Camera drawings of the typical chromatophores 

 of the two sorts make this difference clear. 



Fig. l 



Fig. 2 



Sections of epidermis of larvae of Sana sp. X 450. (Drawn with aid 

 of camera lucida.) 



Fig. A. Tadpole fed on yolk of egg. 

 Fig. B. Tadpole fed on liver. 



