THROWING BACK 89 



pure race of waltzers breed true to their colour and 

 " waltzing " ; but in the second hybrid generation 

 produced from a cross between a waltzing mouse 

 and an albino, there is no association between colour 

 and the waltzing character. The waltzing character 

 is distributed at random over the three colour-groups, 

 A, B and C — i.e. without any preference to any 

 particular colour-group, as can be seen on page 91 

 and Plate II. The numerical proportions in 

 which the various combinations of colour and mode 

 of progression occur will not be considered in detail 

 now ; sufi&ce it to say that rather less than a quarter 

 of the mice in each colour-group, A, B and C, are 

 waltzers. Our attention may now be turned to 

 points of theoretical and practical interest in the 

 results displayed on Plate II. 



To consider the facts from their theoretical side 

 first ; it is seen that the fact of the independent 

 inheritance of the colour and mode of progression, 

 which could not be detected by observing the results of 

 breeding from the pure waltzing race for an unlimited 

 Qumber of generations, is at once revealed (in the 

 second hybrid generation, to be precise) by the simple 

 experiment of crossing two mice which differ in their 

 colour and the mode of their progression. The 

 practical interest of such facts is too obvious to need 

 insisting upon. The number of new varieties in the 

 second hybrid generation is considerable ; and 

 some of them may be counted upon to breed true. 

 The re-combination of characters possessed by the 

 two parents of the cross may be considered first. 



