ENDOCRINE CO-ORDINATION 127 



vertebrae prevents pallor after faradic stimulation of the mouth. 

 In these circumstances the body-cavity may be opened without 

 producing melanophore- contraction ; and when the adrenals 

 of such lizards were stimulated, contraction of the melanophores 

 occurred throughout the entire body after the lapse of only 

 a few minutes. It did not occur, however, in the hind limb 

 after ligature of its arterial supply. When the ligature was 

 removed, on the other hand, the skin of the leg rapidly assumed 

 the condition of extreme pallor. Striking collateral evidence 

 in favour of the possibility that adrenal secretion determines 

 excitement-pallor in reptiles was provided by analysis of the 

 blood-sugar content, which is known to rise in Mammals 

 when adrenalin is Hberated into the circulation, as during 

 excitement ('' emotional glycosuria "). Redfield found that 

 the blood-sugar content was significantly higher in lizards 

 after the production of pallor by nocuous stimulation. To sum 

 up briefly the evidence from these and other experiments 

 bearing on adrenalin, it seems clear : (i) that adrenalin causes 

 the contraction of Reptilian as well as Amphibian melanophores ; 

 (2) that the adrenal glands of Reptiles contain a substance 

 which has the same action as adrenal extracts obtained from 

 Mammalian glands ; (3) that there is indirect evidence that 

 adrenal activity is associated with *' excitement " in Reptiles 

 as in Mammals ; (4) that removal of the adrenals in Phrynosoma 

 in most cases prevented melanophore contraction in response 

 to nocuous stimulation ; and (5) that in addition Reptilian 

 melanophores are capable of direct response. 



The Function 0! the Pituitary Gland.— The part played by 

 secretion of the pituitary gland in determining the normal 

 rhythm of colour-change in amphibia is a further instance 

 of endocrine phenomena of a type which lies outside 

 the province of mammalian physiology. There is reason to 

 believe that adrenalin occurs in the invertebrate phyla. The 

 pituitary gland, on the other hand, is a specifically vertebrate 

 structure from which no active substance has yet been isolated 

 in pure form, so that it is impossible to speculate with profit 

 upon the possible existence of an analogous mechanism in 

 other phyla. In fact, strictly speaking, the pituitary belongs 



