ENDOCRINE CO-ORDINATION 131 



(19 19). Shortly after it was noticed (Huxley and Hogben, 

 1 921) that Urodele larvae exhibit darkening of the skin after 

 pituitary administration, and Swingle (1921) recorded a 

 similar effect after implantation of the pars intermedia in 

 tadpoles. At the same time, the writer initiated a series of 

 experiments on the results of pituitary injection to put to 

 critical test the hypothesis that these effects were due to a 

 freely circulating autocoid of the pituitary gland. 



The results of these preliminary experiments (Hogben and 

 Winton, 1922) may be briefly summarised under four 

 headings : — 



1. The pituitary {p. intermedia and nervosa) of Mammals, 

 Birds, Amphibia, and Fishes, contains a specific stimulant 

 capable of inducing contracted melanophores of adult and 

 larval Amphibia (Anura and Urodela) to undergo maximum 

 expansion. 



2. This property is not shared by such drugs {e.g. histamine) 

 as simulate the physiological action of pituitary extracts in 

 other respects ; nor is it shared by other tissue-extracts 

 examined, namely those of spleen, brain, testis, ovary, pancreas, 

 liver, muscle, adrenal, pineal, and salivary gland. 



3. The melanophore response is a very sensitive indicator 

 of pituitary extracts. The gland of a single frog contains 

 sufficient to induce darkening in some fifty or more individuals 

 of the same species. 



4. The action of the melanophore stimulant in pituitary 

 extract is direct and local, independent of concomitant vaso- 

 motor effects. Taken in conjunction with the phenomena 

 described in Anuran tadpoles by Smith (1920) and Swingle 

 (1921), these data present a strong presumptive case for the 

 view that pituitary secretion forms an important factor in the 

 regulation of Amphibian colour-response. 



In a later series of experiments the effects of removal of 

 the whole pituitary, controlled by comparison with effects 

 of exposure of the brain, section of optic nerves, and removal 

 of the anterior lobe alone were investigated in the common 

 frog (Hogben and Winton, 1925) and analogous experiments 

 to those of Smith and Allen on the axolotl larva of the Mexican 



