W. F. R. Wrldon 
43 
EXPLANATION OF RECORDS. 
In the nomenclature adopted by Weldon, OZfSO (say) represents the eightieth cross of the 
original races, i.e. .Japanese waltzers and ordinary white mice. The resulting ofl'spriug of the 
first litter of this cross are a^, a^, a^, etc., of the second litter of the same cross b^, b-', P, etc., 
and of the third litter c^, c^, c^, c*, etc. The matings of hybrids are denoted by 17/90 for the 
first generation of hybrids, 2JI90 for the second generation and so on. Thus a mouse GHllh- 
denotes that it was the second mouse of the second litter resulting from the 17 mating in 
the 6th generation of hybrids. The characters of any mouse are given by a scheme of the 
following kind : ^ rr£.( i •> r^o i / 1 \ i 
This signifies that the mouse 4i/64c^ was a male ; 75 denotes that the pigmented ai'eas 
covered "75 of the total skin as determined by our scale of pigmented areas (see Plate I). 
q denotes that the eyes are black in this case, p would have marked that they were pink, the 
ordinary albino colour, r and d.r that they were red or dark red corresponding to blood and 
very dark blood colour ; as a rule mice with such eyes have only incompletely albinotic eyes, 
i.e. there is more or less pigment found on dissection. The next three figures in the present 
case, 58, 55 and 1, mark the skin colour of the mouse on the mouse skin pigment scale of the 
Biometric Laboratory. This scale was formed by matching glass mosaics to tlie actual colour's 
of the mouse skins. This scale contains 61 tints. Tints 1 — 9 are the "belly whites," leading 
up to 10 — 18, the palest blue greys; 19 — 27 are pale blue greys; 28 — 33 are yellow; 34 — 39, 
fawn yellow ; 40 — 41 are chocolate ; 43 — 45, chinchilla ; 46 — 54, wild colour of various intensities, 
and 55 — 61, black of various intensities. 
Of the three tints obtained from this scale the first, 58 in our case, marks the colour at the 
centi'e of the median plane of the skin, or if this should fall on a leucotic j)atch in the case 
of the piebald, the tint of the nearest dark patch. The second number gives the colour of the 
skin halfway between the centre of the back and the centre of the belly, 55 in our case ; and 
the third number is that of the colour of the belly. Very often the first two numbers are 
the same, but we found in a good many cases that the tint shaded oft' from centre of the back 
to the belly, and our second number is a rough measure of the lightening of the pigment as 
we proceed from back towards belly. The final symbols given in brackets are Weldon's 
appreciation of the area of pigmentation given by the mnubers 1 to 6 and his appreciation of 
colour as given by the letters a — g, ch. In the case of mice alive at his death and not then 
classed, these colour appreciations and pigment extents were provided as far as possible in 
accordance with his recorded judgments of other mice. 
In the figures on p. 44, reproduced fi'om Biometrika^ Vol. iii. p. 3, Fig. 6 represents a normal 
waltzing mouse. 
Fig. 1 is Weldon's Class 1, more white and less extent of colour patches than a normal waltzcr. 
Fig. 2 is Weldon's Class 2, having about the same amount of colour patches as a normal 
waltzer. 
Fig. 3 is Weldon's Class 3, having somewhat greater extent of colour patches than Class 2. 
Fig. 4 is Weldon's Class 4. 
Fig. 5 is Weldon's Class 5 with only a whitish belly. 
Weldon's Class 6 is a whole colour mouse with nearly the same colour on the belly as on the 
back. Read with a planimeter Weldon's Classes are represented very roughly by ; 
1 2 3 4 5 6 
14 53 68 77 92 100 
We ourselves found considerable difficulty with " whole coloured " mice, and finally arranged 
them in three classes as follows : 
lOO.v are mice with the skin pigmented all over, i.e. the same colour on lielly as on the back; 
100^ are those with a line of paler belly pigment, but not suflicient to take the skin out of the 
6—2 
