(2) Rabbits of the constitution +AA BB EE DD+., _i.e._, agoutis to which a double dose of D has been added are pure blacks in appearance, when only a single dose of D is added the animal shows some agouti markings and is an agouti-black. Such rabbits have always proved to be heterozygous, and when mated together give blacks, agouti-blacks, and agoutis in the ratio 7:6:3. (3) Rabbits of the constitution +AA BB Ee Dd+. An agouti-black (AA BB EE Dd) becomes a pure black when heterozygous for E. Such blacks when mated with blacks of constitution +aa BB EE dd+ throw some agoutis and also some agouti-blacks. Further, the experiments have shewn that the factor +D+ is coupled with +E+ in the gametogenesis of rabbits of the constitution +AA BB Ee Dd+. The gametes produced by such animals are of two kinds only viz--+A B E D+ and +A B e d+. When mated with a tortoise aa BB ee dd they give blacks and yellows only--+and no agoutis+. So far as is known, the coupling between E and D is complete. At present this is the only case of coupling between characters yet worked out in a mammal. [Sidenote: M 3] Experiments with +Poultry+, illustrating the +recombination of characters+. Brown Leghorn [F-] × Silky [M-] | (_a_) Coloured (chiefly brown) | (_a_) White plumage (with or plumage | without slight buff tinge) | (_b_) Normal feathers | (_b_) Silky feathers | _________________________|__________________________ | | F_1 [F-] (_a_) Coloured F_1 [M-] (_b_) Normal feathers --------________ ________--------- --------- × --------- | | | F_2 Generation ________________________________________________________ | | | | /------+------\ /------+------\ /------+------\ /------+------\ Coloured plumage Coloured plumage White plumage White plumage Normal feathers Silky feathers Normal feathers Silky feathers [Sidenote: M 4] Experiment with +Sweet Peas, illustrating reversion on crossing, followed by the appearance of numerous types in next generation+. White × White | F_1 Purple | +---------------------+-------------------+ | | | F_2 3 types of purple 3 corresponding figures Whites viz.:-- of reds, viz.:--