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Show 78 MR. W. BATESON ON COLOUR-HEREDITY [May 26, these qualitative observations are of great value and will provide a basis for future work. In rats the Mendelian rules, in their simplest form, are plainly inadequate to express the facts, and we soon meet a number of deductions of specific application, each needing full investigation. Crampe's account is long and difficult to follow. At first sight also it seems not wholly consistent in certain particulars, but the conclusions here summarised seem well established. Breeding albino rats with wild M. decumanus, Crampe found that Ft might have one of two forms, being either a self-grey like the wild type, or grey with white marks. Unfortunately no precise description of this and of the other broken-coloured rats is given, and we do not know the precise extent and distribution of the white*. According as F2 presented the first or second form, the subsequent offspring produced from F1 bred inter se, differed. The whole series of colours presented by such offspring is arranged by Crampe in seven types, thus :- 1. Self-grey. 2. Grey with white marks. 3. White and grey. 4. White (albino). 5. Black-and-white. 6. Black with white marks. 7. Black without marks. The self-coloured grey in F] gave in their posterity all the types except 3 and 5, but Fx of type 2 gave all seven types. The nature and cause of the heterogeneity in Fx is as yet unexplained. Such an occurrence is, however, not rare. In my own poultry experiments for example, the dark feathers scattered in the white Ft raised between a brown and a white breed may be either chequered or plain black. According as one or the other form appeal's in Fx the posterity probably differ, though this point is not yet established in the case of poultry. The existence of two classes in FT indicates in all probability the existence of two classes of gametes, either in the wild decumanus or in the albinos, but in which we cannot say. From the evidence, it seems that both forms of ~Fl could be produced by the same pair of parents, but I cannot find the fact explicitly stated. Both forms occurred in Fx not only when decumanus was crossed with albino, but also when it was crossed with type 3 and with type 5. Only the albino could cause all seven types to appear in progeny (F2 &c.) raised from a cross with the wild type. The albino was recessive to all the other six types, and albinos of whatever parentage gave nothing but albinos when bred * First crosses shown ine by Miss Douglas were grey except for an irregular but small amount of white on the chest and belly. I take this to be Crampe's type 2. |