14 PIGMENTARY GROWTH AFTER ABLATION OF 



a. Epidermal transplants. 



6. The effect of various pabula upon the pigment cells. 

 c. The response of the chromatophores to various physio- 

 logical and pharmacological agents. 



The chromatophores of albinous larvae 



As is well known, the melanophores of the tadpole are of two 

 types. One type the epidermal melanophore is found in the 

 epithelial covering of the body; the other type the deep melan- 

 ophore lies in or around the deeper structures. These two 

 types, then, of necessity, will be treated independently. 



The epidermal melanophores. The epidermal melanophore, 

 when in an expanded condition, presents an irregularly shaped 

 body from which branched, slender processes radiate for rela- 

 tively long distances (fig. 13). When in a greatly contracted 

 condition, these processes are not evident and the cell body 

 then is of a spherical or slightly irregular shape (figs. 19 and 21). 

 All intermediate conditions between these two extremes can 

 be seen with proper light and temperature conditions. 



The melanophores of the epidermis are greatly reduced in 

 number in the albino (figs. 13 and 14), many counts showing 

 an average reduction of two-thirds from the normal number. 

 Even in a greatly expanded condition these cells are usually 

 separated by wide intervals, a condition which contrasts sharply 

 with that obtaining in the normal animal where the expanded 

 processes unite with, or even overlap, each other. Thirty-one 

 counts from five specimens gave an average of 38 epidermal 

 melanophores in a unit area of 0.36 of a sq.mm. Similar counts 

 from normal animals reveal 119 to this unit area, thus exceeding 

 by over three times the number present in the albino (table 1). 

 It is emphasized, however, that the distribution of these cells 

 in neither type of animal is uniform. Yet their number in the 

 normal even in the areas where they are most thinly distributed 

 exceeds very considerably their number in the albino where 

 they are most thickly placed. Further, the actual melanin 

 content of these cells is diminished in the albino (figs. 13 and 20). 

 Their processes, slender and of light color, present a very differ- 



