350 ACTION OF NATUEAL SELECTION 



has recently been described by H. L. Jameson.* On 

 the north side of Dublin Bay there is a tract of sand- 

 hills, running along the coast for about three miles. It 

 is separated from the mainland by a tidal channel about 

 a quarter of a mile wide at high water, but only 20 

 yards or so at low water. These sandhills are thickly 

 populated with mice, which were noticed by Jameson 

 to harmonise strikingly in colour with the sand. Traps 

 were set, and altogether 36 mice were caught. The 

 specimens varied considerably in the shade of their 

 fur, showing every gradation from the typical Mus 

 musculus of the farmhouses in Ireland and England to 

 individuals with extremely pale dorsal fur usually of 

 a rufous or fulvous gray colour pale buff ventral sur- 

 face, and pale and fulvous appearance of the hairs on 

 the ears, tail, and other parts of the body. Also the 

 feet were white or pale buff, instead of the smoky gray 

 or white of the ordinary House-mouse, whilst the claws 

 were flesh-coloured. Of the 36 specimens, only five 

 were of more or less the typical colour, four were 

 slightly paler, and the remaining 27 markedly palles- 

 cent. 



These mice differ in other characters also. Thus, if 

 the adult specimens be split up into three groups, ac- 

 cording to their colouration, and means taken of the 

 measurements made by Jameson, the values given in 

 the table below are obtained. Though the number 

 of measurements is so small, there can be little 

 doubt that the tail of the palest individuals is 

 distinctly longer than that of the typical ones. Per- 

 haps also the head and body and the hind foot are 

 * Journ. Linn. Soc. (Zool), vol. xxvi. p. 465, 1898. 



