16 REVISION OF AMERICAN MOLES— TRUE. 



general silveriness of coloration. In southwestern Texas the color 

 assumes more or less of a buft" tint, sometimes quite pale and clear and 

 very striking-. 



This alteration, so far as I am able to judge, has nothing directly to 

 do with the color of the soil. The change in Illinois and the surround- 

 ing parts of the Mississippi Valley should be toward black, if the object 

 were to reach a coloration in harmony \yith that of the soil, whereas 

 whatever change is perceptible is in the opposite direction. The altera- 

 tion in the Northwest and Southwest likewise is apparently due to tlie 

 comparative aridity of the regions, the color of the Texan form being 

 diflerent from that of the Northwest, because the parent form is some- 

 what different in color in the two cases. 



On the west coast, as on the east, the change of color is chiefly one 

 of intensity, and runs parallel with the increase or decrease of humidity, 

 as is the case with so many of our mammals. The changes here in 

 Sciqxoius, taken as a whole, are much more striking than those in Sca- 

 lojfs of the East. In the region of great i^recipitatiou, in western Wash- 

 ington and Oregon, the moles are nearly black. In northern California 

 the color is lighter and browner, and in southern California tends to 

 silvery tints. Here again, as far as my observations go, the color of 

 the soil has little to do directly with that of the moles. A soil is, of 

 course, darker when wet than when dry, but the soil about Puget 

 Sound is not especially dark, and certainly does not correspond with 

 the dusky appearance of the moles. 



Possibly we should not expect to find any correspondence, for while 

 the mole is in its burrow its color or that of the soil can be of little 

 consequence. 



We appear to have in the varying intensity of color in moles a purely 

 physiological phenomenon connected with humidity and light. Exactly 

 how humidity affects color is not evident, though there can be little 

 doubt of the faet. So far as I have observed, recent writers, as for 

 examx)le Beddard or Poulton, do not oft'er any explanation of this phe- 

 nomenon, though aware of its occurrence. 



It has to be remembered in this connection that Xeurotrivlms, which 

 is found with Scapanus and Parascalops, and Condylura, which are 

 found with ^Sealojfs, do not change in color in any marked degree. 



VARIATION IN SIZE. 



It is noticeable that in the genera having the smallest range and the 

 least variation in color, the variation in size is also at a minimum. In 

 Cowh/lnra, ParaHcaJops^ and NeurotriclniH there is little variation, while 

 in Scalopti and Scapanus it is marked. In the case of the last two genera, 

 the smallest representatives scarcely exceed one-half the length of the 

 largest. 



So far as the causes of this variation are apparent, they have to do 

 with the food supply. In the case of Scalo2)s, the variation is exceed- 

 ingly gradual on the Atlantic Coast, the size decreasing from north to 



