1903.] IX FANCY MICE AXD RATS. 81 



effected by types 3 and 5, Ciumpe's figures, though too imperfect 

 and irregular to justify a positive statement, show 23retty clearly 

 that these pai-ticular recessives do not appear nearly so often as 

 1 in 4 ; and consequently it \ii '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' I'esoiutions of Antir- 

 rhimmi). 



These are some of the chief deductions apparent from Crampe's 

 work. Many othei's will strike a careful reader and are indeed 

 given by the author, but for these i-eference must be made to the 

 original. 



From the want of details the important question of the identity 

 of the sevei'al types is not easy to settle, but I think that we may 

 allot Crampe's vai'ieties 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 venti'al surlace (togethei- 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 i-epect to the kinds of pigments in luts 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 hah-, especially in 

 the edges of the black patches of the parti-coloured, and on the 

 belly of the self-coloured black. 



No doubt there is also some change with age, moulting, &c.f 

 Orampe (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 refei-red to the hooded and striped types. He 

 remarks that by selecting those with stiipes so wide that the rats 

 wei'e more black than white, he got no nearer to breeding blacks. 

 Similarly whites could not be bred from the whitest gi-ey-and- 



* This is Miss Douglas' experience. In this respect strains doubtless differ, for 

 Mr. P. Swann tells me he formerl}' kept a strain in which the stripe was generally 

 broken. 



f Ci-ampe 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 ' ' Gelh-grau." 



Proc. Zool. Soc— 1903, Vol. II. No. VI. 6 



