A. D. Darbisiiirk 



171 



The view tlial- albiiiisiii is " recessive " in Mendels sense implies that albinus 

 of any aiicostiy, jirovidod thcy tlicniselves are rcally albino, will behave in tlie 

 samo way when crossed. Now, tho yi)ung of all the albinos are not tlie saine and 

 at the enil of niy last paper it was pointed out that a differcnce in the kind of the 

 litter corresponded to a difference in the anccstry of the albino niother : that is to 

 say, that wild-cohjnred mice only appeared in the littors of pure-bred albinos: 

 and the genoralization that the more in-bred a nioiise was, the less power it 

 had of transmitting its whiteness, was suggested. The evidence brought forward 

 for this were the results of von Gnaita who in four Grosses between waltzing mice 

 and albinos which were in-bred for 29 generations always got absolutely wild- 

 coloured niiec ; and my own results consisting of nine such Grosses. This 

 generalization is borne out liy the additional eleven litters which have appeared 

 since my last paper was written ; as a Classification of litters into (a) those 

 from cross-bred albinos and (6) those from pure-bred albinos will readily shew 

 (Table IL). 



TABLE IL 



In my previous paper I think I did not sufficicntly emphasize the difference 

 which seems to me to exist between in-bred and pure-bred mice : the above table 

 is certainly of pure-bred mice ; but what is not certain is whether the relative 

 inability to transmit whiteness among pure-bred mice is due to the fact of their 

 being pure-bred, or in-bred. Pure-bred mice usually are in-bred and von Guaita's 

 unquestionably were ; but this does not help us to decide whether the relative 

 inability to tran.sinit whiteness is due to in-breeding or pure-breeding ; it only 

 shews that it is not impossible that it may be due to in-breeding. The meanings 

 of these terms shoukl be clearly understood : there are two pairs of categories, one 

 pair in which cross-bred is antithetic to pure-bred, and auother pair iu which 

 out-bred is antithetic to in-bred, the former pair referring to the presence or 

 abseuce of any other colour than white in the ancestry of the mouse, the latter 

 pair to the distance or uearness of relation of the parents, grandparents, etc. of the 

 mouse under consideration. And before the cause of the great preponderance of 

 the number of wild-coloured mice in the litters of pure-bred over the number 

 of those in the litters of cross-bred albinos can be ascertained waltzing mice must 

 be crossed with in-bred and out-bred pure-bred albinos and in-bred and out-bred 

 cross-bred albino.s. (Such kinds of albinos are being reared as quick lyas possible.) 

 Whatever the explanation be, the fact remains that the ancestry of a white mouse 

 does make a difference in the character of its offspring when crossed with a 

 waltzinir mouse. 



* The 60 iu the table ineludes the 7 yellow mice Ha iu whicli there is no wlüteness. 



22—2 



