310 ALFRED C. REDFIELD 



secretion and direct nervous action. It may be concluded, 

 therefore, that the nervous control of the melanophores is of 

 secondary importance to the coordinative action of adrenin upon 

 these cells. 



b. The nervous paths of melanophore reflexes. The nervous 

 system may be explored readily in search for the paths over which 

 the impulses induced by noxious stimuli travel to the melano- 

 phores, by cutting awa}^ various parts of it and then attempting 

 to produce a contraction of the melanophore pigment by stimu- 

 lating the animal. 



Decerebration does not interfere with the reaction of melano- 

 phores to noxious stimuli. After the entire brain anterior to 

 the cerebellum has been cut away, horned toads recover and ]> ay 

 live many days. The melanophore pigment becomes expanded, 

 but may be caused to contract by stimulating the surface of the 

 cloaca with an induced current of electricity. If the spinal cord 

 is sectioned at the level of the second vertebra, stimulation of 

 the cloaca may still produce a contraction of the melanophore 

 pigment. It is evident that the medulla and the anterior part 

 of the cord are unnecessary for the reaction. If the cord is cut 

 at the level of the twelfth vertebra, or destroyed completely 

 posterior to this level, stimulation of the mouth by a weak induc- 

 tion current will produce a distinct contraction of the melano- 

 phore pigment. The posterior portion of the cord is thus un- 

 essential for the completion of the reflex. There remains the 

 portion of the spinal cord which lies between the second and 

 twelfth vertebrae, part of which appears to be necessary for the 

 contraction of the melanophore pigment which follows a noxious 

 stimulus. It has been pointed out in another place (p. 300) that 

 if the cord is destroyed between the eighth and twelfth vertebrae 

 noxious stimuli are no longer able to bring about this reaction. 

 The portion of the cord between the second and eighth vertebrae 

 is not capable of bringing about a contraction of the melanophore 

 pigment. It appears that in the region between the eighth and 

 thirteenth vertebrae are located nervous structures, perhaps 

 'nerve centers/ through which those nerve impulses pass which 

 cause a contraction of the melanophore pigment. 



