MELANOPHORES OF THE HORNED TOAD 295 



The foregoing experiment must be carefully controlled, for 

 it is quite conceivable that blood from any horned toad might 

 have an effect upon the melanophores of another individual, 

 irrespective of the presence of hormones in it. That this sup- 

 position is untenable is indicated by the following experiment: 



August 4, 1916. 12.30 P.M. Hypodermic needle inserted into the 

 lymph space under the skin of the left side of a horned toad the pigment 

 of which is expanded. 



1.42 P.M. Injected through the needle 0.2 cc. of defibrinated blood 

 drawn by quickly decapitating a second horned toad. This decapitated 

 animal had had a portion of the thoracic spinal cord destroyed, an opera- 

 tion which prevents any noxious stimulation from producing a con- 

 traction of the melanophore pigment (see p. 300). In this way the 

 presence of the suspected hormone is avoided. The first animal still 

 had its pigment expanded. 



1.53 to 3.00 P.M. No change in the color of the first horned toad. 



Since the exclusion of blood from a part of a horned toad during 

 excitement causes the melanophore pigment of that part to remain 

 expanded, and since the injection of blood from an excited horned 

 toad into an unexcited individual causes the melanophore pigment 

 of the latter to contract, it may.be concluded that the melano- 

 phores of the horned toad are influenced by a hormone, present 

 in the blood during nervous excitement, which causes the melano- 

 phore pigment to contract. 



c. The nature of the hormone involved in melanophore reactions. 

 What is the chemical substance which causes a contraction of the 

 melanophore pigment of the horned toad and where is it produced? 



The conception of a hormone regulating the activity of melano- 

 phores is not altogether novel. Fuchs ('14, pp. 1546 to 1547, 

 1651 to 1652) has attempted to explain the behavior of pigment 

 cells in amphibian larvae and reptiles by assuming that sub- 

 stances, perhaps internal secretions, which contract the pigment, 

 are produced in the body under the regulation of the pineal organ. 

 Laurens ('16) has recently shown this hypothesis to be inap- 

 plicable to the phenomena observed by him in Ambylstoma 

 punctatum. 



The pineal body of the horned toad (Phrynosoma douglassii 

 and Phrynosoma coronata) has been described by Ritter ('91), 



