ino.{.] 



SCIENCE. 



403 



willi i)ink eyes has usually sumtty (brown- 

 pisrniented ) ears, nose and feet: and a race 

 of mice with pink eyes, thouy:h partially 

 piufniented coat, has formed the basis of 

 some recent important experiments in he- 

 redity conducted by Darbishire (:02, :03) 

 at Oxford, Engrland. These exceptional 

 conditions probably represent stable coup- 

 liners of a part only of the dominant char- 

 acter (pigrmented coat) with the recessive 

 character (white coat), and are similar in 

 kind to the DR character of spotted mice. 



Further, coupling may occur between a 

 number of characters greater than two, 

 so that they form, to all intents and pur- 

 poses, in heredity, one indissoluble com- 

 pound character. Thus, Correns (:00) 

 observed that in crosses between two species 

 of stocks {Mathiola incaiia DC. and M. 

 glabra DC.) the second generation hybrids 

 showed reversion to one or the other of the 

 parental forms in all three of the principal 

 differential characters studied, viz., hairy 

 or glabrous stems, violet or yellow-white 

 flowers, and blue or yellow seed. A blue 

 seed always produced a hoary plant bear- 

 ing violet flowers; a yellow seed always 

 produced a glabrous plant bearing yellow 

 or white flowers. 



4. Disintegration of Characters. — This is 

 the converse of the foregoing process. Not 

 only may characters apparently simple be 

 coupled together in heredity to form com- 

 posite units of a higher order, but charac- 

 ters which ordinarily behave as units may 

 as a result of crossing undergo disintegra- 

 tion into elements separately transmissible. 

 Thus the gray coat-color of the house- 

 mouse is always transmitted as a domin- 

 ant unit in primary crosses with its white 

 variety; but in the second cross-bred gen- 

 eration a certain number of black mice ap- 

 pear, some or all of which are probably 

 hj'brids. For similar black mice obtained 

 by crossing l)lack-\\ hiti' with white mice 



have been shown, by breetling 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. Ac- 

 cordingly black mice clearly belong with 

 grays in the category of dominant individ- 

 uals [D or D (R)], but they have visibly 

 only the bla^k constituent of the gray coat, 

 the remaining constituent, a rufous tint, 

 having been separated from the black in 

 consequence of cross-breeding. There is 

 reason to believe that the rufous consti- 

 tuent may become recessive. ('. c, 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 com- 

 posite coat-color of the 'Belgian hare,' 

 when that animal is crossed with ordinary 

 white rabbits, the result being the produc- 

 tion of black, j^ellow and mottled indi- 

 viduals, 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 investiga- 

 tion. 



Correns ( :00) mentions a case in plants, 

 which probably belongs in this same cate- 

 gory. In crossing the blue-flowered (dom- 

 inant) 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 tliis case the i-ecessive 

 character, rather than the dominant, un- 

 derwent disintegration. 



ii. Departures from the Theoretical 



