MELANOPHORES OF THE HORNED TOAD 319 



From these considerations it may be anticipated that, like 

 the smooth muscles of the mammahan body, the melanophores 

 of Anolis possess a double innervation from the two divisions of 

 the autonomic nervous system. It may be that such a condition 

 is present quite generally among those vertebrates whose melano- 

 phores are under nervous control. If such a condition exists, it 

 may have escaped detection because the nerve-trunks contain 

 fibers of both sorts, and when they are simulated one sort, usually 

 the sympathetic, dominates over the other in its effect upon the 

 pigment cells. 



If the preceding discussion has succeeded in demonstrating the 

 resemblance between the control of melanophores and smooth 

 muscles by the autonomic nervous system and the adrenal 

 glands, it has lent strong support to the hypothesis of Spaeth 

 ('16a) that the melanophores are functionally modified smooth 

 muscle cells. 



c. The physiological basis of the emotions. Cannon ('15) and 

 his collaborators have shown that the mechanism underlying the 

 usual emotional manifestations in man and the other mammals is 

 the autonomic nervous sytsem and its important adjunct, the 

 adrenal glands. It has now been sho\\Ti that in the horned toad 

 this same mechanism is brought into play during nervous excite- 

 ment. The basis for emotional manifestations appears to be the 

 same in reptiles as in mammals. The mechanism must be one of 

 great antiquity, for Gaskell ('14) has discovered the location and 

 activity of the chromaffin (adrenal) system in the leech and 

 certain other annelids. Whether this system is at this time 

 connected in any way with phenomena corresponding to the 

 emotions of the higher animals cannot be stated. 



VII. SUMMARY 



1. The reactions of the melanophores of the horned toad pro- 

 duce a series of color changes correlated with the rhythm of day 

 and night, an adaptation of the color of the skin to that of the 

 environment, and a characteristic pale condition of the skin 

 during nervous excitement (pp. 278 to 280). 



