46 COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 



every case except that of the albino. Yet we have seen that red and 

 yellow animals, which have no black pigment in their coats, do not 

 transmit black coat-pigment to their offspring, though they do transmit 

 black eye-pigment. We might conclude that eye-pigment is something 

 altogether different from and independent of coat-pigment, but two 

 considerations negative this idea: (i) Black-eyed white animals mated 

 with albinos produce animals with coat-pigment in the typical patches, 

 a thing which neither parent possessed ; (2) in mice, animals with coat 

 patches but devoid of eye-pigment, when mated with unrelated albinos, 

 produce offspring with pigmented eyes, again a character which neither 

 parent possessed (Darbishire, :O4). From these facts we see that a cer- 

 tain connection does exist between eye-pigmentation and coat-pigmenta- 

 tion, though apparently it is less close than that between one coat-patch 

 and another coat-patch. The disappearance of eye-pigmentation, like 

 the disappearance of coat-pigmentation, is probably due, in the case of 

 ordinary albinos, to latency in the germ of a particular hereditary unit. 

 This condition of latency, it is evident, can be made to disappear by 

 cross-breeding with any animal of the centripetally pigmented type. 

 But in centripetally pigmented animals, as we shall see, disappearance 

 of eye-pigment, when once it has occurred, is apparently beyond recall, 

 at least by cross-breeding with albinos. This is indicated by the instruc- 

 tive experiments of Darbishire ( : 04), which we shall presently examine 

 more in detail. 



A condition which might be described as semi-latency of a coat- 

 pigment was observed in the case of a red-white animal, 9 9 r 5? which 

 was mated with red $ 1019. To my great surprise she produced in 

 two successive litters four young having black-red coats. This was 

 contrary to any previous experience (compare Table G), and I at once 

 sought for an explanation. Upon looking the animal over carefully 

 I found, what I had before overlooked, that she had a sacral patch of 

 black skin, though not a single hair of her body, so far as I could dis- 

 cover, was black pigmented. The capacity to form black integumen- 

 tary pigment was evidently present in the animal, though its influence 

 extended only to the epidermis proper, not to the hair-follicles. One 

 often sees in dogs, for example in fox-terriers, black skin spots of this 

 sort in body regions where the coat is entirely white. The character 

 semi-latent in 9 915 came into full activity in four of her offspring 

 by a male devoid of that character. 



Black skin is not infrequently seen on the feet of red guinea-pigs, 

 but such animals do not produce young with black hairs when they 

 are mated with other red animals. A comparison of this result with 

 that described in the case of ? 915 serves to emphasize the distinction 

 which has been made between centrifugal and centripetal pigmentation 



