THE HOUSE MOUSE 641 
Several specimens of a pale buff or cream variety were sent to 
W. Evans from Lyne, Peebles, where they occurred in some abundance, 
in April 1890. 
Varieties with long, black, silk-like hair (W. P. Cocks, Rep. R. 
Cornwall Polytech. Soc., 1852, 59); naked, with corrugated skin (a few 
whiskers present), and producing similar young (Bateson, Varzatzon, 
56); partially naked and smooth-skinned (?disease or parasites; 
Gordon, Zoologist, 1850, 2763) have been recorded. Cocks (Bucks 
and Zoologist, 1903, 420) mentions an epidemic of blind and par- 
tially blind House Mice captured during a succession of years in one 
locality. 
Pigmentation and inheritance :—When examined microscopically, 
under a low power, the hairs of the back are seen to be of three kinds, 
although all have slender bases and fine distal, terminal points. Some 
(Fig. 94) are short and fine, constituting the underfur. Others are 
of medium length, flattened and broadly expanded centrally ; these 
apparently correspond with the spines found in the fur of rats. 
Lastly, many are very long and show two or three expanded tracts 
alternating with contracted portions (Fig. 94)1; the terminal expansion 
of these hairs is usually bright yellow in colour, but the fine tips 
together with the lower portions are black or dusky. To these longer 
hairs the general colour is due. The belly is clothed only with the 
short hairs of the underfur. 
The minute structure of the hairs is, as in many other rodents, of a 
remarkably complex type. Each hair consists as usual of an outer 
sheath or cortex of kerotin investing a central medullary cavity ; when 
highly magnified, the latter is seen to be divided into compartments by 
slender bridges of kerotin. At the base of a hair the bridges are 
transverse and the compartments simple; but in the broader parts, and 
particularly in the “spines,” the bridges acquire an oblique direction, 
and send forwards and backwards outgrowths of kerotin which join 
similar processes from the contiguous bridges; by this means in such 
places the transverse medullary compartments are divided into two, 
three, four, or five separate secondary chambers (Fig. 94). The 
number of secondary chambers to a transverse compartment increases 
as the hair expands, and diminishes again as it tapers distally.” 
1 Douglas English describes and figures similar alternately contracted and 
expanded hairs in the Shrew (Some Smaller British Mammals, 66). 
2 This structure attracted attention in the earliest days of microscopy. Thus 
Shaw (General Zoology, ii., Pt. 1, 57, 1801) describes the hairs as “appearing 
internally divided into a kind of transverse partitions, as if by the continuation of a 
spiral fibre.” He further cites Derham (1657-1735), who, in his Physzco-Theology, 
conceived that this mechanism of a spiral fibre may serve for the “ gentle evacuation 
of some humour out of the body,” and added that “perhaps the hair serves as well 
for the insensible perspiration of hairy animals as to fence against cold and wet,” 
