PIGMENT CHANGES IN ANURAN LARVAE 131 



similar view of a normal (light-colored) animal. The difference in 

 the degree of expansion of the pigment cells is obvious. Figure * 

 10 shows the expansion of the deep-lying melanophores in the 

 meninges of the brain in an engrafted specimen. 



As previously mentioned, Hooker ('14) states that the epider- 

 mal melanophores are non-contractile, and although this may be 

 true of the form with which he worked, it is apparently not the 

 case with young Rana catesbeiana larvae. In skin preparations 

 of this species, both in whole mounts and in sections, it is evident 

 that in light-yellow individuals the expanded epidermal type of 

 melanophore is very scarce and difficult to find. This is excep- 

 tionally well shown in whole mounts of the skin. The subepider- 

 mal cells are found to be contracted and present the appearance 

 of black balls, with little indication of cellular structure. On the 

 other hand, whole mounts of the skin of darkly colored engrafted 

 tadpoles show two distinct layers of chromatophores, a superfi- 

 cial and a deep, lying at different levels. The upper layer or epi- 

 dermal melanophores form a definite network, with the cell proc- 

 esses of neighboring cells in contact, thus giving the appearance 

 of a recticulum (fig. 6, also fig. 4). The deeper layer of pigment 

 cells (subepidermal) are greatly expanded and present the famil- 

 iar 'mossy' appearance characteristic of this phase of the cell. 

 It seems to the writer that, unless the epidermal melanophores 

 possess the power of contractility, it is otherwise difficult to 

 explain why light-colored animal show so few of these cells, while 

 in engrafted individuals they are not only very numerous, but 

 their processes give the appearance of an anastomosing network. 

 In sections through the skin, similar conditions are seen ; the epi- 

 dermal melanophores are numerous, with long cell processes in 

 deeply pigmented engrafted larvae, but very sparsely scattered in 

 the epidermis of the light-colored controls. Judging from condi- 

 tions in my material, it seems that these pigment cells are more or 

 less contractile, though evidently not to the extent that the larger, 

 subepidermal melanophores are. They apparently increase in 

 number, or at any rate become visible with elongate processes in 

 engrafted animals, thus playing an active part in the color 

 change following transplantation of the pars intermedia. 



