MENDEL'S LAW AND THE HEREDITY OF ALBINISM. 389 



a unit without serious disturbance of the balanced relationship of pigmented and 

 unpigmented areas in the mosaic structure. This tendency is observable in eighty- 

 four of the one hundred and fifty-four cases recorded. Of the remaining seventy 

 cases, sixty-seven are quite comparable with our own. In sixty of them the black 

 character, latent in one or possibly in both parents, has become active and combining 

 with yellow (fawn) visible in the pigmented parent, has formed gray. In seven cases 

 black, if present, has remained latent, and the offspring are simply yellow-pigmented. 

 But in the case of three black and of six black-white hybrids, this curious result is 

 observed: the pigmented character (yellow) visible in the dark parent disappears 

 entirely, while black takes its place. 



In Darbishire's experiments, as in our own, the effect of a cross with albinos 

 is to release the dominant character from the strict localization which it had in the 

 mosaic parent. In Darbishire's mosaic mice the localization of pigment was much 

 more rigid than in our own. His mice bore pigment only on the shoulders and rump 

 and had pink eyes; ours were pigmented over at least half of the body and had black 

 eyes. It is not surprising, then, that the pigmentation should be less extensive in 

 Darbishire's hybrid mice than in our own. Yet it is evident that in all his hybrids 

 there occurred release, more or less complete, of the pigment-forming character from 

 its localization in the original mosaic. In every case the hybrid had pigmented eyes, 

 though neither parent possessed this character. 



V. PURE AND HYBRID MOSAICS. 



In our experiments in crossing spotted with albino mice, a third black-white 

 male was employed. He was a half-brother to the two spotted males previously 

 mentioned, born of the same mother but by a different sire. The white areas on his 

 body were less extensive than those on his two brothers. He was bred to the same 

 stock of white females as they, but with different results. By him the albinos bore 

 albino as well as pigmented offspring; of the former twenty-one, of the latter twelve, 

 ten being gray and two black. The albino offspring were found in this case, as in 

 all others tested, to breed true inter se. 



It is evident that the third black-white male differed in nature from his two 

 half-brothers, for he formed recessive gametes, whereas they did not. 



Examination of other breeding records of spotted mice kept by us during the 

 past two years shows that it is possible in these also to distinguish two different sorts 

 of mosaic individuals. These are: 



