1903,] IN FANCY MICE AND RATS. 97 



the cross with wild grey gave grey F^. (2) Albinos extracted 

 from the cross with black gave hlach F^. (3) Albinos extracted 

 from a cross with yellows (of complex origin) gave a mixture in 

 Fj, either of yellovjs and greys^ or of yellows and blacks. There 

 is therefore a proof that individual albinos, though outwardly 

 alike, may belong to several distinct classes, exhibiting dijSerent 

 properties in their heterozygous unions (cf. Parsons' case, p, 84). 

 The resemblance of the heterozygote to the coloured type from 

 which the albino was exti-acted is a new fact, the significance of 

 which we cannot yet fully appreciate *. Cuenot tentatively makes 

 the attractive suggestion that the particular colour of the hetero ■ 

 zygote may depend on the association in the same zygote of vaiious 

 colour-constituents ; and that though the albino is white in itself, 

 it may carry on such constituents from a previous coloured pai'ent. 

 Then, accoixling as one or other of these complementary consti- 

 tuents is brought in by the albino, the heterozygote will show the 

 corresponding colour. The chief obstacle to this view is the fact 

 that when a heterozygote shows I'eversion (as opposed to simple 

 dominance) the reversion frequently inckides various qualities, 

 such as size, temperament, habit of growth, &c., as well as coloui'. 



A cognate problem was alluded to (p. 88) in the discussion of 

 von Guaita's facts. His original black-and-white x albino gave a 

 reversionary heterozygote ; yet in F^ both the black-and-white and 

 the grey-and-white DRs present those colours as simple dominants 

 over albino, as their offspring proved. Since in this case no new 

 strain was introduced, the reference to pedigree is not sufficient 

 to elucidate the whole difficulty. 



The relation of the several classes of albinos to each other seems 

 to be the next point for investigation, and a useful experiment 

 might be made by breeding albinos extracted from one colour, with 

 albinos extracted from another colour, the offspring to be then 

 tested with a single pure coloured race. It is not impossible 

 that the various types of albino will then themselves exhibit 

 phenomena of segregation. 



The new report of Mr. Darbishire (28) and Professor Weldon's 

 comment (29) have appeared too late for adequate discussion here. 

 It may, however, be remarked that both authoi-s scarcely appreciate 

 the Mendelian view when they state that according to it all 

 albinos (or other recessives) may be treated as "in every respect 

 similar." ISTo one, I imagine, would suppose that the similarity 

 need extend to characters other than the albinism. We are 

 familiar with cases in which recessives, though alike in the i-eces- 

 sive character, are dissimilai- in other respects ; and (as stated stcpra 

 p. 76) may, when crossed together, even produce heterozygotes 

 exhibiting a character known to be dominant over the particular 

 recessive concerned. We should no more suppose all albino mice 

 to be identical because they were albino, than all white sweet-peas 



* Possiblj' it is to this phenomenon that Crampe refers in the statement discussed 

 on p. 79 of this paper. I cannot, however, find a case of Crampe's exhibiting 

 Cuenot's phenomenon. 



Proc. Zool. Soc— 1903. Yol. II. No. YII. 7 



