COLOR AND ITS INHERITANCE IN GUINEA-PIGS. 



The experiments described in the following paper were carried on 

 at the Bussey Institution of Harvard University, between September 

 1912 and August 1915, under the direction of Professor W. E. Castle. 

 A large number of stocks of guinea-pigs and wild cavies, containing an 

 extensive assortment of variations, were available throughout the 

 experiments, and furnished excellent material for studies on inheritance. 

 The writer wishes here to express his gratitude for the privilege of using 

 freely this material and for the constant encouragement and assistance 

 which Professor Castle has given. 



SKIN, FUR, AND EYE COLORS OF GUINEA-PIGS. 



COLOR OF CAVIA CUTLERI. 



The fur color of Cavia cutleri, the probable ancestor of the guinea-pig, 

 is of the agouti type found in most wild rodents, as well as in many other 

 wild mammals. (See plate 3.) The back and sides are slaty black, ticked 

 with yellow (more accurately, cinnamon buff). An isolated hair is of 

 a dull slate color at the base, becoming blacker toward the tip. Near 

 the tip there is a yellow band some 2 or 3 mm. long. The extreme tip 

 for 1 to 2 mm. is black. The belly is cream-colored (more accurately 

 cartridge buff) and is sharply separated from the ticked sides. An 

 isolated hah* is pale neutral gray throughout its basal half and cream- 

 colored in the remaining portion. Cavia rufescens of Brazil has a 

 similar ticked coat, but differs in showing less ticking on the back and 

 sides and often in having a ticked belly not sharply separated from the 

 sides. The general appearance is darker. Tame guinea-pigs show a 

 great variety of colors and color patterns and also deviations from the 

 dark skin and black eye color of the wild species. 



MELANIN PIGMENT. 



The coat colors of mammals are largely due to granular pigments of 

 a kind known chemically as melanin. The pigment in the hair is 

 found principally in the walls of air-spaces in the medulla, but to some 

 extent in the cortex, as described by Bateson (1903) in mice. Melanin 

 pigments are also found in the skin (principally in the epidermis) and 

 in the iris and retina of the eye. A deficiency of pigment in the retina 

 is revealed by a red reflection through the pupil. 



PRIMARY CLASSIFICATION OF FUR COLORS. 



Three qualitatively distinct melanin pigments are generally recog- 

 nized in mammals, viz, black, brown, and yellow (Bateson, 1903) . There 

 are reasons, however, for regarding black and brown as more closely 

 related to each other than either is to yellow. Black and brown 

 granules are acted upon similarly by most hereditary factors which act 



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