318 ALFRED C. REDFIELD 



investigators do not appear to have pressed the idea of double 

 innervation of the melanophores. 



It has been pointed out (Carlton, '03) that the melanophore 

 pigment of Anolis, unlike that of other vertebrates, is expanded 

 by impulses from the autonomic nervous system. This excep- 

 tional behavior might be explained in one of two ways. It might 

 be assumed that these melanophores are under the control of the 

 sympathetic division of the autonomic nervous system, and that 

 tKese nerves affect the melanophores of Anolis by causing the 

 expansion of the pigment instead of the contraction that they 

 cause in other animals. Parallels to this condition are not lacking 

 in mammalian physiology, for the sympathetic division causes 

 a contraction of some smooth muscles (in the blood-vessels) and 

 relaxation of others (in the intestinal walls), as Elliott ('05) and 

 others have abundantly shown. Sympathetic impulses may 

 have antagonistic effects even in the same organ, according to 

 Dale ('06). If such is the condition in Anolis, one might expect 

 adrenin, which mimics the action of the sympathetic division, 

 also to cause an expansion of the melanophore pigment. This, 

 however, is not the case; it is stated on page 316 that adrenin 

 causes the melanophore pigment of Anolis to contract. It seems 

 doubtful, therefore, if the melanophore pigment of Anolis is 

 expanded by impulses from the sympathetic division of the 

 autonomic nervous system. 



The alternative explanation is to assume that the melanophore 

 pigment is expanded by impulses from fibers which are physiolog- 

 ically analogous to the cranial-sacral division of the autonomic 

 nervous system of mammals. If such be the case, adrenin 

 would be expected to cause the opposite effect upon the melano- 

 phores, which indeed it does. This supposition harmonizes 

 with the facts completely. It vasbj further be argued, since 

 adrenin causes a contraction of the melanophores of Anolis, 

 that these cells are also innervated by the sympathetic division 

 of the autonomic nervous system, and that these fibers cause 

 the pigment to contract, for Elliott ('05) has shown that the 

 reaction to adrenin is an excellent indicator of the presence and 

 nature of sympathetic control of a tissue. 



