452 MURID^— AGRESTIS 



of the allied M. arualis produced five young in captivity at the 

 age of eighty-eight days on 2nd March, five more on 6th July, 

 and again five on 30th July. The latter opened their eyes 

 when ten days old. On the 12th day, though still very small, 

 they began to leave their nest. On the 26th day they appeared 

 to be nearly "grownup." In other respects the breeding habits 

 are not known to differ from those of other mice, it being uncer- 

 tain whether they are monogamous or- not. Probably in this 

 respect their customs are as loose as in other gregarious mammals. 



The voice, often used in moments of excitement or hunger, 

 is half a grumble, half a squeak.^ They do not seem to chatter 

 their teeth and stamp their feet as some exotic species do. 



In captivity these mice are far more amiable than Bank Mice. 

 Perhaps owing to poor brain power, they become tame very 

 soon after capture, and can with difficulty be teased into biting. 

 The young have been reared by a Field Mouse under the care 

 of Mr F. H. Parrott^ and by a House Mouse.^ 



They are good swimmers. Mr Rope* has disturbed one 

 amongst seaweed cast up by the tide, when it made for the 

 water and swam out boldly. Mr Bruce Campbell has 

 observed^ some swimming for pleasure in the sea in the 

 Firth of Forth, at Long Green Bay, Dalmeny. 



Charles Darwin comments upon the dependence upon each 

 other of Dutch and red clovers, humble-bees, and "field mice."'* 

 The clovers are fertilised by the bees, and the numbers of the 

 latter in any district depend in a great measure on the number 

 of "field mice," which destroy their combs and nests, according 

 to Colonel Newman, to the extent of two-thirds all over England. 



Darwin believed, again, that the number of mice is regulated 

 by the number of cats, but here the correlation is doubtful ; his 

 remarks are often read as referring to Field Mice,^ but the facts 

 are probably true of several species, and the Grass Mouse is 

 the most common in situations where humble-bees nest. Grass 

 Mice also destroy a destructive sawfly,^ which damages larch.^ 



' W. Evans. ^ Cocks. ^ Rope, Zoologist, 1883, 332. 



' Zoologist, 1890, 330. ° Ann. Scott. Nat. Hist, 1901, 48. 



" The Origin of Species, 6th ed., 37th thousand, 1883, 57. 

 ' Apodemus sylvaticus. ^ Nematus erichsonii of Hartig. 



" An exhibit to illustrate this fact was shown at the Royal Society's conversazione 

 on 13th May 1908, by C. G. Hewitt. 



