THE PITUITARY REGULATION OF MELANOPHORES IN THE RATTLESNAKE

¹ The Department of Zoölogy, University of Wyoming, Laramie, Wyoming

1. In the prairie rattlesnake, Crotalus v. viridis Raf., the background of the skin is a homogeneous yellow-white color reflected from the evenly distributed dermal guanophores. The dark pattern of this snake is formed by various distributions of melanophores and pigmented epidermal cells superimposed upon this background.

2. Two main types of melanophores are found in the skin. One is relatively small and resides primarily in the epidermis; the other is much larger, structurally different, and retains its cell body in the dermis, but sends its ramifying processes into the epidermal layer.

3. Both of these melanophores appear to be associated with the deposition of melanin granules in the keratinizing portion of the epidermis, since (a) the distribution of its melanin deposits coincides with the pattern of the underlying melanophores, and (b) the rate of pigment deposition is greatly reduced after hypophysectomy.

4. The removal of the pituitary or the pars intermedia alone causes a permanent paling due to the complete concentration of the melanophore pigment. This paling, however, is more evident after the shedding of the old keratinized epidermal layer carrying previously deposited melanin.

5. Intraperitoneal injections of intermedin from the chicken pituitary will produce complete melanin dispersion in the melanophores of an hypophysectomized animal.

6. Preliminary observations on four other species of snakes indicate a similar pituitary regulation of the epidermal melanophores.