MELANOPHORES OF THE HORNED TOAD 307 



clear contraction of the melanophore pigment of the left leg, which 

 brought out in sharp contrast the dark and light bands (fig, 14) . 



These experiments have been repeated many times. In no 

 case has stimulation of the spinal nerves produced any contrac- 

 tion of the melanophore pigment. The results of stimulating the 

 sciatic nerve are extremely variable; often no contraction of the 

 pigment is produced. In many individuals, however, stimulation 

 of fibers which occur in the sciatic nerve produced a contraction 

 of the melanophore pigment. 



Many attempts have been made to isolate various portions of 

 the skin from the central nervous system by cutting through the 

 nerves supplying these parts. The sciatic nerve has been cut 

 in the thigh, groups of spinal nerves have been severed close to 

 the spinal cord, and cuts have been made through the body wall 

 so as to isolate completely portions of the skin in the manner 

 described on page 288. In no case have these operations altered 

 ^he reactions of the melanophores of the isolated regions in any 

 way. The responses of the melanophores to direct stimulation 

 and to hormones evidently suffice to bring about all ordinary 

 melanophore reactions without the aid of nerves which connect 

 with these cells directly. 



One operation of this type has yielded a pertinent observation. 

 When the spinal cord of a horned toad is transected at about 

 the level of the thirteenth vertebra, the melanophore reactions are 

 ordinarily unaffected in every way, except that a noxious stimulus 

 applied to the posterior part of the body no longer produces a 

 contraction of the melanophore pigment. Under usual laboratory 

 conditions, the skin of such animals remains in a uniform dark 

 condition. Three cases have been found to which the foregoing 

 statement does not apply. On the day following the operation 

 these horned toads had recovered fully, but the condition of the 

 melanophores was exceptional. On the anterior half of the back 

 the melanophore pigment was completely contracted, giving this 

 portion of the skin the maximum pale condition. Posterior to 

 the point at which the cord had been sectioned, the melanophore 

 pigment remained fully expanded. The skin of this portion was 

 quite dark (fig. 15). 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 26, NO. 2 



