ENDOCRINE CO-ORDINATION 121 



indicate that the melanophores are subject to direct nervous con- 

 trol. In Amphibia and Reptiles there is as yet no histological 

 proof of innervation of the pigmentary effector system ; and, 

 as v^^ill be seen, there exists an alternative method of interpreting 

 the regulation of pigmentary changes. We shall first consider 

 the significance of the adrenal glands to the colour responses of 

 reptiles. A word or two may be inserted with reference to the 

 comparative physiology of adrenaline, concerning which there 

 are a few observations which suggest further lines of inquiry. 

 Adrenaline in the Animal Kingdom.— Oliver and Schafer 



Fig. 30. — Action of adrenaline on the heart of Pecten. 



(1895) fi^st discovered that the adrenal medulla of the 

 mammal yields an extract which has a powerful pressor action 

 on the circulation of the mammal. Later the researches of Lew- 

 andowsky, Langley, and Elliott showed that in general adrenal 

 medullary extracts, or adrenaline, the active substance isolated 

 by Takamine, produces the same effects upon plain muscle in 

 vertebrate animals as the stimulation of the sympathetic 

 nerves, e.g. inhibition of intestinal tone and rhythm, dilatation 

 of the pupil and constriction of the arterioles in all verte- 

 brates and acceleration of the heart in mammals and birds. 

 It is, however, to be noted that the action of adrenaline is 



