544 PROCEEDINGS OP THE AMERICAN ACADEMY. 



white with white mice have been shown, by breeding tests, to be hybrids, 

 since on crossing with white mice they produce white mice, black mice, 

 and, in one or two cases, gray mice also. Accordingly black mice clearly 

 belong with grays in the category of dominant individuals [D or D (R)], 

 but they have visibly only the black constituent of the gray coat, the re- 

 maining constituent, a rufous tint, having been separated from the black 

 in consequence of cross-breeding. There is reason to believe that the 

 rufous constituent may become recessive (i. e. latent) either in the black 

 individuals or in the reverted whites, or in both. It is seen separated 

 from both the black and the white characters, in the chocolate-brown and 

 reddish-yellow individuals obtained in cross-breeding. 



A fancier of rabbits tells me that there occurs a similar disintegration 

 of the composite coat-color of the " Belgian hare," when that animal is 

 crossed with ordinary white rabbits, the result being the production of 

 black, yellow, and mottled individuals, in addition to ordinary gray- 

 browns. 



The various distinct colors or color patches of the guinea-pig have 

 doubtless originated in a similar way, — by resolution of the composite 

 coat-color of the wild Cavia, upon crossing with an albino sport. This 

 subject is now undergoing investigation. 



Correns (:00) mentions a case in plants, which probably belongs in 

 this same category. In crossing the blue-flowered (dominant) Mathiola 

 incana with the yellowish-white flowered (recessive) M. glabra, the 

 second generation recessives produced in some cases pure white flowers, 

 in others yellow flowers. In this case the recessive character, rather 

 than the dominant, underwent disintegration. 



5. Departures from the theoretical ratios of dominants to recessives. 

 Considerable departures are to be expected when the number of offspring 

 taken into consideration is small, but with increase in the number of 

 offspring examined, the departures should grow less. This is usually 

 found to be true. Mendel's numbers are shown by Weldon (:02) to 

 be well within the limits of probable error. But certain cases have been 

 observed in which departures of a particular sort persist even with con- 

 siderable numbers of offspring. Thus Allen and I have found the 

 recessive character, white, in mice to be inherited in about three per cent 

 more than the calculated number of cases, while the equally recessive 

 dancing character is inherited in about thirty-three per cent less than the 

 calculated number of cases. These fairly uniform departures indicate, 

 to my mind, a vitality, on the part of the recessive gamete, in one case 

 somewhat superior, in the other much inferior to that of the dominant 



