342 THE POPULAR SCIENCE MONTHLY 



these poisoned parts, the sympathetic nerves. For these reasons I be- 

 lieve that in Anolis the inward migration is a process which is ordinarily 

 under the control of the chromatophore itself and that the outward 

 migration, which takes place all over the animal when even only a small 

 spot in the skin is illuminated (Parker and Starratt, 1905), is depend- 

 ent upon the action of sympathetic nerves. 



In the true Chameleon, as Briicke (1852) and many others have 

 demonstrated, precisely the reverse is true: the outward migration is 

 independent of nerves and the inward migration is produced by them. 

 Moreover, judging from the results of experiments on the spinal cord, 

 the nerves which in Chameleon are concerned with these changes are not 

 sympathetic nerves, but spinal nerves. 



These differences between Anolis and Chameleon I believe to be well 

 founded. In my opinion both animals have descended from a stock 

 in which the chromatophores were entirely independent of nervous 

 control and in the process of descent the chromatophores of different 

 lines became separately appropriated as effectors of the nervous system. 

 In the ancestors of Anolis the sympathetic nervous system became re- 

 lated to the outward migration of pigment; and in those of the Chame- 

 leon the spinal system associated itself with the inward migration. 

 The fact that Chameleon and Anolis belong not only to separate 

 families, but to separate suborders of lizards, rather emphasizes this 

 view than otherwise. 



Such instances as the independent retinal chromatophores of Palce- 

 monetes and the nervously dependent chromatophores of Chameleon 

 and Anolis lead me to believe that chromatophores are effectors evolved 

 independently of nervous control, but in some cases secondarily appro- 

 priated as nervous end-organs. 



What has been said of chromatophores so far as their relation to 

 nerves is concerned is probably also true of glands. The majority of 

 glands are unquestionably independent of direct nervous control. In 

 almost all instances a blood supply is essential to the action of a gland, 

 and as this can be controlled by nerves there is thus an indirect influ- 

 ence of the nervous system on the action of the gland, but this nervous 

 control over the blood supply is very different from a direct nervous 

 control over secretion. I know of no good reason to assume that nerves 

 have any direct influence on the secretions of the kidneys, the liver or 

 even the pancreas. The pancreatic juice which appears with such pre- 

 cision on the arrival of food in the small intestine has been shown by 

 Bayliss and Starling (1904) to be secreted not through the action of 

 nerves on the gland, but through the action of a substance, secretin, 

 produced by the food in the intestine and carried by the blood to the 

 gland. If into the blood of a fasting animal whose nerves to the pan- 

 creas have been cut a small amount of secretin is injected, the pan- 

 creas will begin to produce its characteristic secretion. 



