2 Result of Crossing Japanese Waltzing with Albino Mice 
The individuals of each group can also be classified according to the colour of 
the coloured patches. 
Class a = yellow. 
Class b = fawn yellow. 
Class c = pale wild colour 1 • , p , 
^ y , I.e. that of the house-mouse. 
Class d = dark wild colour J 
Class e = black. 
Class / = " lilac " — pale blue grey ; at present only exhibited by the offspring 
of hybrids. 
Class g = chocolate. 
The letter "p" after a mouse indicates that it has a pink eye, the letter " W" 
that it waltzes; to take two examples, 2b (pW) is a waltzer, 6d or 6c is a house- 
mouse. 
I propose to defer a detailed discussion of the nature of these categories to a 
later date : but I hope the foregoing remarks will leave no doubt in the reader's 
mind as to what is meant by each class ; in fact, all the classes except the first 
two explain themselves. I am sorry the word fawn was used in my second paper, 
because it is used to denote both a and b by mouse fanciers ; a is simply a yellow 
colour ; b is yellow, with, in many cases, black in it ; at any rate, there are inter- 
mediate stages linking b with c (i.e. pale wild), whereas a is not so linked with c 
except through b. 
In cases of intermediate colours the mice are entered 56c and so forth : a 
minute discussion of the skins (which are kept) is deferred. 
Methods of Registering. 
The method of keeping, registeriug and cataloguing which I now pursue has 
gradually grown up of itself in the course of a year rather as a result of necessity 
than by deliberate invention on my part. Lack of a proper method of registering 
at the beginning of the experiments rendered many of the dealings with mice a 
matter of great difficulty ; and I suggest that if the reader is taking up work of 
this kind he will not suffer from a similar inconvenience if he adopts a method 
similar in prinoi})le to that which I am about to describe. 
During the latter part of the experiment there were some fifteen hundred mice 
in the room set apart for the purpose ; and it was quite a simple matter to look up 
in the catalogue book any mouse in the room, and vice versa, to find in the room a 
mouse of any given ancestry. The method is very simple, and was based on a 
system of cross-reference, which enabled one to refer (as already stated) from the 
books to the mice, and from the mice to the books. 
The following account, then, will be of little if any interest to the reader who 
does not intend to do similar work. 
