104 CALIFORNIA ACADEMY OF SCIENCES [Proc. 4th Ser. 



areolar tissue, may be seen in many sections. Free granules of red 

 color aid in giving the red color to the extended throat-fan. 



The skin is extremely vascular but more so in some regions than 

 in others. Larger vessels run beneath the denser connective 

 tissue layer and run parallel with it, dipping into the scale. From 

 these vessels branches are given off which run through the denser 

 connective tissue and also through the leucophore layer to 

 directly supply the epidermis (Fig. 13). It seems not improbable 

 that a vaso-dilatation occurring under and in the leucophore 

 layer, may exert a modifying influence on the color states. The 

 pink color of the mid-dorsal stripe may be explained by the effect 

 of a vaso-dilatation on a white stripe, and the red appearance of the 

 throat-fan is no doubt in part due to blood, as well as to granules 

 of red pigment in the subcutaneous connective tissue, which shows 

 through the spaces between the scales. 



On the Mechanism of the Color Changes 



The essential structures present for the production of the 

 various color states are the epidermis, the yellow oil droplet layer, 

 the leucophore layer, the melanophores, and, possibly, the zantho- 

 phores and the cutaneous blood supply. 



The skin of the scale is made up of four superimposed, inverted, 

 hollow, cup-like layers, the outer being the epidermis. Next to 

 this is the oil droplet layer, then the leucophore layer, and lastly, 

 the connective tissue layer which, however, supports the integrity 

 of the whole. 



The first and last named layers are continuous with those of the 

 neighboring scales, but the second and third are limited to the 

 scale. 



The epidermis is a transparent layer which acts largely as a 

 protecting and supporting structure and, through interference 

 phenomena, acts slightly, if at all, as a factor in the color states. 



The second or yellow oil droplet layer presents a thin trans- 

 parent yellow mediimi which is extremely important in the pro- 

 duction of many of the color states. In and superficial to it lie 

 the fine terminals of the branches of the melanophores. The large 

 zanthophores also lie in it and extend inward into the next layer. 

 The oil droplets give a strong, bright color by transmitted light, 

 but seem to reflect but little light (Fig. 10 A and B). It seems to 

 act more as a filter than as a reflector. White light reflected from 



