130 W. W. SWINGLE 



as Allen stated, but in older animals the corial sheet of pigment 

 cells appears much as in normal larvae and persistent contraction 

 of the melanophores does not occur. The silvery appearance of the 

 pituitariless animals is due primarily to reduction in number and 

 melanin content of the epidermal melanophores and the persis- 

 tent expansion of the layers of xantholeucophores. 



The contraction and expansion of the melanophores throughout 

 the body following hypophysectomy in the first instance and trans- 

 plantation of the gland in the second, is to be expected. It would 

 be odd, indeed, if only the superficial melanophores were affected 

 by the hormone, or activating substance of the pars intermedia. 



Fixed and stained preparations of the skin and other tissues 

 were employed as a means of checking conditions observed in the 

 living tadpole. Whole mounts and sections of the skin were both 

 used, the skin being taken from the dorsal surface of the body. 

 Because pigmentary conditions are more readily followed in the 

 skin than in other tissues, the discussion is chiefly confined to 

 changes occurring in the epidermal and subepidermal melano- 

 phores. 



It was observed in sections through the skin and in whole 

 mounts of skin from the experimental animals that the subepi- 

 dermal pigment cells were greatly expanded, their processes ex- 

 tending like branches of a tree through the stratum spongiosum of 

 the corium. Expansion is so great that the processes of the differ- 

 ent cells interlace to form a very dense pigment sheet. In figure 

 3 A is shown a section through the skin illustrating this point. 

 The much-branched melanophores are shown cut in various 

 planes by the microtome knife. Figure 35 shows the condition 

 presented by the light-colored control larvae. Here the subepi- 

 dermal melanophores are shown as much contracted masses lying 

 in the corium. Transverse sections are not so good for illustrat- 

 ing expansion and contraction of the melanophores as are surface 

 views of the integument in which the entire cell appears instead 

 of portions of it. Figure 6 shows a photomicrograph of the 

 melanophores of an engrafted animal from a surface view of the 

 skin, or rather a section cut obliquely in such a manner that 

 practically a surface view is obtained, and in figure 5 is shown a 



