XII, B, 4 Ruth and Gibson: House Lizards 183 



shades between the two extremes of a creamy white to a taupe 

 (the darkest gray) with a slight brownish tinge. Under normal 

 conditions this lizard changes its color from one extreme to 

 another in about thirty minutes. Upon irritation by shaking in 

 a Petri dish, the time for changing from a dark to a light color 

 can be greatly lessened, approximately fifteen minutes being 

 necessary foj* the "contraction" of the melanophore. Redfield 

 has observed similar results in the horned toad during states of 

 nervous excitement and believes that this coordination of the 

 contracting melanophore must be due to a hormone, which is 

 probably "adrenin." 



A number of experiments were performed to determine, if 

 possible, the normal condition of the melanophore when at rest, 

 whether it was then expanded or contracted. In one series of 

 lizards the eyes were removed under ether ansethesia, while in 

 others the cerebrum was removed, and in still others the spinal 

 cord was severed. The eyeless lizards assumed a dark color 

 irrespective of the color of the background and surroundings. 



In the decerebrated lizards similar results were observed both 

 as to their indifference to react to background stimulation, dark- 

 ness, and light. However, the latter, if mechanically irritated, 

 would always turn a light color, and the melanophores would be- 

 come "contracted." Laurens says that the eyeless Amblystoma 

 larvae do not respond to difference in background, though they 

 do respond to light stimulation; this is quite the reverse from 

 what is found in lizards. The melanophores of the eyeless 

 Amblystoma larvse, when kept in light, are fully expanded, and 

 when kept in the dark, the subepidermal melanophores are 

 maximally contracted. 



If it be true that there is an actual "contraction" and "expan- 

 sion" of the melanophore, then the aggregated central mass 

 of pigment granules should have greater dimensions in the "con- 

 tracted" than in the "expanded" cell. In the bleached lizards, 

 many melanophores were seen as minute pigmented points only. 

 Other cells persist, apparently of the normal expanded type, evi- 

 dently unaffected or only slightly affected in the normal bleaching 

 reflex. However, we have also made measurements of the cen- 

 tral masses in such persisting cells in cleared sections of skin; 

 when compared with similar measurements of the central masses 

 of the melanophores of the normally dark lizard, the former were 

 usually less and never greater than the latter. 



When cleared sections of dark, light, and the intermediate 

 shades of lizard skin were examined under the oil immersion, 

 the details of the melanophore could be easily seen. The center 



