612 PROCEEDINGS OF THE AMERICAN ACADEMY. 



to albinos produced only pigmented offspring. These offspring, though 

 not themselves spotted, were clearly hybrid mosaics, for when bred inter 

 se they produced spotted as well as albino offspring, of the former nine, 

 of the latter fourteen, in a total of forty-four young; the expectation on 

 our hypothesis is eleven of each ! 



The idea that there are, as just explained, two different sorts of mosaic 

 individuals, originated with the junior author of this paper. It constitutes 

 a discovery of no small importance, one which lends strong support to 

 the IMendelian hypothesis of essential gametic purity. It shows that 

 alternative parental characters, when united in fertilization, do not mix, 

 but that each retains its own identity and subsequently separates from 

 the other when gametes are formed. This takes place even when one of 

 the parental characters is itself a mosaic/ Herein we have a confirmation 

 of the conclusion based upon morphological observations, that the pa- 

 ternal and maternal contributions to the zygote retain each a distinct 

 individuality. Further, the idea of Bateson receives confirmation, that 

 the gray color of mice obtained by crossing black-white with white mice 

 is itself a " heterozygote " character. 



Darbishire's premature conclusion, that in his spotted hybrids " albinism 

 is not recessive," will undoubtedly be abandoned by him when he has 

 reared from them a second generation of hybrids. From our own ex- 

 periments and those of von Guaita we confidently predict that he will 

 obtain approximately one in four of albino mice, and of the pigmented 

 mice obtained, part will be pure mosaics (as defined by us), but a larger 

 part will be hybrid mosaics like their parents.* 



* This prediction has been fulfilled sooner than we liad expected. In a paper 

 just received Darbishire (: 03) states that his hybrid mice bred inter se have 

 produced 66 young. Of tliese 13 are albinos, and 17 are (in our terminology) 

 pink-eyed mosaics, while the remaining 3G have dark eyes. The last named class 

 consists clearly of hijbnd mosaics like their parents. The Mendelian expectation 

 is that half the offspring, or 33, will be of this sort; the observed number is 36. 

 The other two classes (albinos and pure mosaics) should theoretically number 16.5 

 each, or together 33 ; they number 13 and 17 respectively, or together 30. 



The correctness of this interpretation of Darbishire's results can easily be tested 

 by further breeding of his animals. The pink-eyed individuals, if really pure mo- 

 saics, as we suppose, will, when bred to albino individuals, produce only dark-eyed 

 offspring; whereas their dark-eyed brothers and sisters when similarly mated will 

 produce botli dark-eyed individuals (like themselves) and albinos, in approximately 

 equal numbers. Further, the pink-eyed individuals will probably breed true inter 

 se, whereas dark-eyed individuals will continue to produce in subsequent genera- 

 tions, as in the case already observed by Darbishire, offspring of three sorts, 



