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Show 1903.] IN FANCY MICE AND RATS. 81 effected by types 3 and 5, Crampe's figures, though too imperfect and irregular to justify a positive statement, show pretty clearly that these particular recessives do not appear nearly so often as 1 in 4 ; and consequently it in prima facie likely that some of the new types of gametes are formed by imperfect segregation, and are combinations containing elements of both the dominant and the recessive-a phenomenon indicated by experiments with other forms of animals and plants {cf. de Vries' resolutions of Antir-rhinitm). These are some of the chief deductions apparent from Crampe's work. Many others will strike a careful reader and are indeed given by the author, but for these reference must be made to the original. From the want of details the important question of the identity of the several types is not easy to settle, but I think that we may allot Crampe's varieties among the well-known types of rats, with fair confidence, as follows :- 1. The wild decumanus. 2. Like decumanus, but with a more or less sharply defined white area on the ventral surface (together perhaps with white on the feet). 3. Head and shoulders wild colour, forming the " hood" of the fanciers. This is continued in a broad stripe down the middle of the back to a patch on the rump. The rest of the body is white. The coloured area may be considerably extended on to the flanks, and more rarely * the dorsal stripe may be broken. 4. Albino. 5. Like 3, but black being substituted for wild colour. 6. Like 2, but black instead of wild colour. This type is known in the fancy as the " Irish " variety. 7. Self-coloured black. With repect to the kinds of pigments in rats I have as yet no information. The distinction between black and the wild colour is apparently less sharp than in mice, and both black and black-and- white rats have a good deal of dark brown hair, especially in the edges of the black patches of the parti-coloured, and on the belly of the self-coloured black. N o doubt there is also some change with age, moulting, &c.t Crampe (9. p. 393) mentions the black stripe in his black-and-whites, and there is practically no doubt that his var. 3 and var. 5 are correctly referred to the hooded and striped types. He remarks that by selecting those with stripes so wide that the rats were more black than white, he got no nearer to breeding blacks. Similarly whites could not be bred from the whitest grey-and- * This is Miss Douglas' experience. In this respect strains doubtless differ, for Mr. F. Svvann tells m e he formerly kept a strain in which the stripe was generally broken. f Crampe records (9. p. 395) changes with age in piebalds from " grey " to black and vice versa, both colours appearing together in the transition. The change in the direction of darkening seems to be normal as the adult fur grows. In the same place he mentions a rat as " Gelb-grau." PROC. ZOOL. Soc-1903, VOL. II. No. VI. 6 |
