50 



Messrs. J. S. Huxley and L. T. Hogben. 



stimuli received through the organs of vision. How this control is exerted is 

 at present an unsolved problem. 



Two possibilities invite consideration. Either the stimuli received by the 

 eyes are transmitted entirely through the nervous system via the fibres 

 innervating the pigment cells — assuming that in all cases pigmental cells are 

 innervated from the C.N.S. ; or nervous stimulation of internal secretions 

 efficient to produce the appropriate reaction may be involved. Obviously 

 both mechanisms may operate concurrently. In order to interpret the 

 pigmental responses in these animals in a manner consonant with the second 

 hypothesis, it is first necessary to demonstrate that the melanophores react in 

 one way to one type of internal secretion and in an opposite sense to another. 

 It has been stated that a pituitary hormone causes the melanophores to 

 expand ; and the question arises whether other internal secretions can bring 

 about the reverse effect. In this connection two observations provide a clue. 

 McCord and Allen (19 L7) have recorded that after feeding tadpoles (Rana 

 sylvatica) on pineal glands for 10 days, each subsequent meal was followed by 

 transient, and complete, contraction of melanophores, noticeable in half-an- 

 hour, reaching its maximum in about 45 minutes, and passing off after 2 to 

 3 hours. Bigney (1919) again finds that by injecting adrenalin into the adult 

 frog, the contraction of the pigment cells is produced, confirming earlier 

 work of Lieben (1906). 



To test the reaction of the pigment cells in Axolotls to pineal treatment, 

 eight medium-sized (9 month) larvae were placed (November, 1920) in separate 

 containers, of which the sides had been blackened, and illuminated from above. 

 In this way maximum expansion of the pigment cells is brought about within 

 a few hours. Four were fed on fresh pineal glands tri-weekly, and the 

 remaining four (controls) were kept on a normal meat diet. The experiment 

 was continued for 2 months and proved quite fruitless. No pigmental 

 differences either of a permanent or temporary character could be observed 

 in Axolotls, although, as will be seen later, McCord and Allen's observations 

 as to the effect of pineal feeding on tadpoles were afterwards confirmed. Two 

 similar experiments with the same numbers were then repeated, with adrenal 

 medulla instead of with pineal gland ; whether administered as food or by 

 adding fresh extract to the medium, a complete contraction of the pigment 

 cells invariably ensued, with great vaso-dilatation of the gills.* 



It thus appears that the pigment cells of medium-sized Axolotls react in an 

 opposite manner to pituitary and adrenal extracts, and the fact that in Allen's 

 experiments the removal of the pituitary was accomplished by melanophore 



* Probably the effect is in either case due to adrenalin acting on the skin vid the 

 medium. 



