COAI IN HYBRIDS OF PEROMVSCUS EREMICUS. 39 



est liair> of the sample, i.e., the maximum hair length of this re- 

 gion, was determined in each case. 



It was already known that the general coat color of the individual 

 n the proportional .lumber of different types of hairs 

 in the pel - well as upon the relative length of the subter- 



minal yellow band in the " agouti " hairs and some other charac- 

 If. therefore, the color differences between these various 

 geographii - of mice were due to differing combinations of 



.delian unit-factors, such factors would be more likely to re- 

 n the hereditary behavior of these more element- 

 ary (1, an in that of the mass effects, as shown by pho- 

 of considerable areas of the pelage. To what de- 

 : at all. this theoretical expectation has been realized, will 

 1-e r. 



In the following pages, we shall deal with these mass effects 

 t'ir-t, before proceeding to a consideration of the various micro- 

 hair characters which form their basis. This seems the 

 1 1 ii in- logical order to follow, despite the fact that in the case of 

 this particular series of skins the microscopic studies preceded 

 the photometric ones. 



II. GENERAL COAT COLOR AS DETERMINED BY THE TINT 



PHOTOMETER. 



I IK- !l<~--Ives Tint Photometer and its use in the study of 

 mammalian pelages have already been discussed briefly by the 

 senior author in several previous papers. 1 Pending the prepara- 

 tioi e adequate account of this procedure, a very brief re- 



statement of the technique employed must suffice. 



A rectangular area of the pelage, together with an equal area 



" -tan. laic 1 " white, are viewed in juxtaposition through three 



suo lor screens (red, green and blue-violet). In each 



. the light from the standard white is cut down by a shutter 



until the luminosity (and necessarily the color as well) is equal 



hat of the object under examination. The readings of the 



lever controlling- this shutter, which are expressed in hundredths, 



furnish tli from which the color and luminosity values here 



employed are computed. 



i 1 nents see Sumner <M. E.rf. Zool., 







