296 ALFRED C. REDFIELD 



who finds it to be a highly developed organ, in part closely 

 resembling an eye. The structure of the epiphysis, with its 

 folded epithelial walls containing great quantities of blood cor- 

 puscles, does not forbid the interpretation that it may function 

 as a gland of internal secretion. It may be readily shown, how- 

 ever, that it is not the organ concerned, primarily at least, with 

 the production of the melanophore hormone. The skull of a 

 horned toad may be trephined and the entire brain anterior to 

 the cerebellum, and including the pineal organ, may be removed. 

 The animals recover from this operation and their pigment be- 

 comes fully expanded. Stimulation of the cloaca with a weak 

 induced current is still able to produce a contraction of the 

 melanophores. 



A more favorable clue to the identity of the melanophore hor- 

 mone is found in the work of Cannon and his collaborators 

 (Cannon, '15). Cannon and de la Paz ('11) have demonstrated 

 that during states of emotional excitement there is an increase in 

 the concentration of adrenin in blood drawn from the adrenal 

 vein of the cat. A similar increase is produced by stimulation of 

 sensory nerves and by asphyxia (Cannon and Hoskins, '11), 

 conditions which will be shown to produce a contraction of the 

 pigment of the horned toad. It is well known that adrenin 

 occupies an especially significant place in the physiology of smooth 

 muscle. Langley ('01), Elliott ('05), and others have shown that 

 the action of adrenin upon this tissue in a great number of cases 

 is identical with the effect of stimulating the sympathetic fibers 

 innervating the smooth muscles of the body. Spaeth ('16a) 

 has concluded that melanophores ' ' are to be considered function- 

 ally modified smooth muscle cells." He has accumulated evi- 

 dence which shows at least that there is a very close analogy 

 between the two types of cell. 



In view of these facts, it would not be surprising to find that 

 adrenin is the hormone concerned in coordinating the melano- 

 phores of the horned toad. 



It has been pointed out by Coronae Moroni ('98), and by Lieben 

 ('06) that adrenin produces a contraction of the melanophore pig- 



