THIRD EEPOPiT ON HYBPIDS BETWEEN WALTZING 

 MICE AND ALBINO RACES. 



ON THE UKSULT OF CROSSINd .) AI'AXlvSl-: WALTZIXG MICE 

 WlTil "EXTRACTED" RECESÖiVE ALBINOS. 



Bv A. I). DARBISHIRE, Balliol College, Oxford. 



A.s is well kiiown to those fannliar with this (juestion, it is an esseutial part of 

 the Meiulcliaii hypotliesis that tliu (so-called "extracted") recessive individual 

 which is producod by pairiiig two first cro.sses, is in every rcspcct simiiar to tlie 

 original pure recessive. It forms, in fact, the foundation oti which the doctrine 

 of the purity of the germ-cells rests. To put the matter niore e.xplicitly, the 

 extracted recessive is ideutical with the original pure recessive and is not afFected 

 by its unusual ancestry in any way. 



It is the object of the present report to doscribe three ditferent kiuds of 

 crosses which shovv that the character of the offspring of extracted albinos is 

 determined by (or at any rate correlated with) the ancestry of the albino parent. 



I have crossed jjure-bred waltziiig niice, not witii pure-bred albiuos, but with 

 extracted recessive albinos : now, tlie offspring tlius obtaiued are either correlated 

 with their grandparents (i.e. the hybrid parents of the albino), or, they are not. 

 Tiiat is to say the character of the graudparent either has some effect on the 

 character of the graudchildreu or it has not. 



I hope the following cases will show that it has. 



1. Pure-bred waltzing mice were crossed with albinos produced by pairiug 

 two first crosses together. Tlius : 



Waltzer Albino Waltzer Albino 



^7~^ — ' ^ — 1 — ' 



First Gross First Gross 



Waltzer x Albino 



