COAT CHARACTERS IN GUINEA-PIGS AND RABBITS. 9 



ordinary white one which has become dirty. For a long time I so 

 accounted for the condition seen in a particularly unattractive albino 

 in my flock, but finding that no change occurred in her coat, I investi- 

 gated the case with the result noted. So-called Himalayan rabbits 

 are albinos with peripheral pigmentation similar to that just described 

 for cavies. But there occur also albino rabbits without peripheral 

 pigmentation. In the Himalayan rabbit, as in the albino cavy, the 

 coat of the young is commonly white at first all over the body, but 

 soon becomes pigmented at the extremities. In some cases the first 

 coat on the general body surfaces is slightly pigmented also, the pig- 

 ment being found chiefly in the hair tip. This pigmentation is already 

 forming at birth, and can be recognized by the deeper red color of the 

 skin, as compared with that of normal individuals. 



I have never seen a case in which this pigmentation of the hair-tips 

 persisted in the adult animal, though that of the extremities regularly 

 does. It is apparently in rabbits restricted to the first coat, though in 

 guinea-pigs it is found only in the later coat. 



It is difficult to formulate a satisfactory definition of an albino mammal. \ 

 Absence of pigment is the most obvious characteristic of albinos ; yet, as / 

 we have seen, many albinos possess a considerable amount of pigment. 

 Furthermore, experiment shows that black-eyed white cavies, which 

 produce no pigment whatever in the coat, nevertheless transmit very dif-^ 

 ferent hereditary pigment potentialities from those of albinos. Accord- 

 ingly the amount of pigment produced in the coat is not distinctive^ 

 between albinos and other animals ; neither is the absence of pigment 

 from the eyes distinctive, for Darbishire ( : 04) has experimented with 

 a race of pink-eyed mice which when crossed with albinos behave 

 every way like ordinary pigmented ones. 



Without attempting a complete analysis of the matter, for which J 

 present knowledge does not suffice, I would suggest the following as / 

 criteria which, so far as observed, separate albino mammals sharply/ 

 from all others. An albino is an animal with unpigmented eyes and\ 

 with little or no pigment in its coat. The pigment, if present, is found/ 

 in greatest amount at the extremities of the body. In a word, the pig-\ 

 mentation of an albino is essentially centrifugal. When by selection OB/ 

 cross-breeding the pigmentation is reduced, it is reduced centrifugally. 



But in animals not albinos, the pigmentation is centripetal. Reduc-\ 

 tion of the pigmented areas takes place in this case toward well- ' 

 marked centers, as has been pointed out by Allen ( : 04) in the case of 

 mice. From a study of spotted mice Allen was led to recognize for that 

 animal five paired pigment centers situated dorso-laterally, as follows : 

 (i) genal or cheek center, (2) nuchal or neck center, (3) scapular or 

 shoulder center, (4) pleural or side center, and (5) sacral or rump cen- 



