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, Variation, 

 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) ^ ; 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.^ 



' Douglas English describes and figures similar alternately contracted and 

 expanded hairs in the Shrew {Some Smaller British Mammals, 66). 



''■ This structure attracted attention in the earliest days of microscopy. Thus 

 Shaw {General Zoology, ii., Pt. I, 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 Physico-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." 



