Chromatophores and Color Change 713 



omy. Hypophysectomized Anolis remain permanently bright green"'^ (Fig- 

 274). They no longer darken in response to black background or bright 

 light. They can be darkened readilv by injection of extracts of whole pi- 

 tuitary of hshes or the intermediate lobes of frogs or reptiles. The melano- 

 phores of the rattlesnake appear also to be normally dispersed by a prin- 

 ciple from the pituitary. '"'■* 



Transection of nerves, such as section of the spinal cord at various levels, 

 or cutting the sciatic nerve in Anolis, in no wav interferes with the normal 

 color responses. In fact, attempts at histologic demonstration of nerve termi- 

 nations at the melanophores have been uniformly unsuccessful. Skin grafts 

 verv soon show color changes which are svnchronous with those of the host. 

 Exclusion of the blood supplv from anv region, on the other hand, results 

 in a paling of that region in about 15 minutes. 



The roles of the animal's own hypophvsis and adrenals can be shown by 

 electrical stimulation with one electrode placed in the cloaca, the other in 

 the mouth. Stimulated pale animals kept in darkness become uniformly dark 

 brown. Denerxated areas respond just as do the innervated ones. Similar 

 stimulation of hypophysectomized specimens gives, on the other hand, a char- 

 acteristic mottling of the body. This last is not obtained after both adrenal- 

 ectomv and hvpophysectomv. Furthermore, injection of adrenalin or of ex- 

 tracts in Ringer solution of the animal's own adrenals produces the typical 

 mottling. Adrenalectomized animals lighten in response to a white back- 

 ground. All of these observations, and others, point strongly to the con- 

 clusion that the melanin in Anolis normallv disperses as a result of the ac- 

 tivity of a principle from the intermediate lobe, and that its gradual disap- 

 pearance from the circulation suffices to account for lightening. Rapid 

 blanching which normally follows electrical stimulation or excitement may 

 perhaps be accounted for by integumentary vasoconstrictor activity and un- 

 der some circumstances bv the production of adrenin. 



Light appears to have no significant influence on the melanophore state 

 in intact Anolis, other than through the eyes. 



The available evidence indicates roles of both nerves and hormones in the 

 melanophore responses of the iguanid, Phrynosoma. The early work of Red- 

 field^ ''^ on this form has been largely confirmed and considerably extended 

 bv Parker.^'^"* These animals are normally gray with characteristic black 

 patches. The latter patches show no color changes, whereas the intervening 

 area varies with appropriate stimulation from dark gray to pale grayish- 

 white. These changes are due primarily to melanophore activities. Darken- 

 ing of the animal occurs in about 15 minutes, and lightening in approxi- 

 mately twice that time. 



Phrynosoma darkens on an illuminated black background, at low tempera- 

 tures, and in response to very strong illumination. It lightens on an illum- 

 inated white background, at high temperatures, and in darkness. 



The melanophores are normally under the influence of pigment-concen- 

 trating nerve fibers. Stimulation of a sciatic nerve will induce lightening in 

 the corresponding hind leg. Electrical stimulation of the roof of the mouth 

 or of the cloaca results in a paling of the whole animal, which is quickly re- 

 versible. Following denervation of a region of the body, leg, or lateral trunk, 

 similar stimulation results in a lightening of all regions except the denerv- 



