6 Result of Crossing Japanese Waltzing with Albino Mice 
Description of Parents. 
Japanese Waltzing Mice. 
These animals are distinguished from ordinary (say albino) fancy m.ice by 
their smaller size, by their extreme liability to disease, but especially by their 
curious habit of spinning round, by the ceaseless movement of their heads, and 
by the retrograde motion of the body when not waltzing. The mice used by me 
had pink eyes, and bore patches on the body of colour indicated by h : the range 
of variability in colour was practically nothing ; that of the extent of the coloured 
patch was small : accurate pictures have not been kept of all of them because 
the simple Mendelian statements, which it was the original object of the experi- 
ment to test, did not lead to the expectation that minute study of these mice 
would be necessary ; the exact distribution of the colour on the waltzing parent 
is therefore not known in all cases ; in those cases in which pictures of the 
waltzers were made, a classification of them has been made into (a) vvaltzers with 
less colour than Fig. 7, and (/S) waltzers with more colour than Fig. 7. All the 
waltzers used were of pure strain. 
Albino Mice. 
In the previous experiments of this kind (conducted by von Guaita) the albinos 
used were of ixniform ancestry, being in-bred for 29 generations ; that is, they were 
also pure-bred. I obtained my albino stock chiefiy from Mr Steer in England, 
from M. Jeunet in Paris, and from Herr Fockelmann in Hamburg. From the 
pure-bred mice which I got from Mr Steer I raised in-bred pure-bred albinos, and 
by mating the foreign mice with English ones I obtained out-bred pure-bred mice. 
An out-bred pure-bred mouse would have this ancestry for example : 
3 from Jeunet x ? from Steer ? from Fockelmann x s from Broxup 
Albino (out-bred pure-bred) 
Out-bred cross-bred mice were obtained by crossing black or yellow mice with 
albinos — in-bred cross-bred were obtained by waiting for a litter, from such a 
cross, in which there were both albinos and blacks (or yellows), then pairing a 
black mouse with his white sister, and so on for many generations. 
A list of all the mice bred during the experiment is given in Appendix I., 
Tables A to H. 
The Hybrids. 
Before describing the results of crossing albinos and Japanese waltzers, I think 
it is advisable to define clearly the terms which I shall use to describe each 
generation. The offspring produced by crossing a Japanese waltzer with an albino 
I propose to call the hybrid, simply ; the offspring of these hybrids paired together, 
