1903.] NATURAL SCIENCES OF PHILADELPHIA. 297 



but where much moisture is carried over the coast belt and up the 

 river valleys by the persistent fogs which sweep in from the Pacific 

 ocean. 



The region occupied by E. hammondi is exceedingly dry, with a 

 rainfall of less than 10 inches, and tliis species is relatively constant 

 and is not known to show any tendency to melanism.^* 



'* That humidity in some way influences the metabolic processes which lead 

 to pigmentation can hardly be doubted. Temperature need scarcely be con- 

 sidered in the present case, for the dry region, extending from Arizona to nortliern 

 Montana, and to considerable elevations, has a very great thermal range, while 

 the wet region is relatively equable. There is a suggested connection between 

 the large amount of uric acid produced by reptiles and the fact that the yellow 

 and orange coloring matter from the wings of certain butterflies has yielded a 

 substance closely related to uric acid, but physiological chemistry is not yet 

 competent to explain how these waste products are converted into pigments. 



The liberty to indulge in the striking colors developed in the garter snakes of 

 this region is partly due to the protection afforded by luxuriant vegetation, and 

 perhaps in some degree to the absence of the three snake-eating genera Spiloies, 

 Ophibohcs and Elaps. 



