A New Field-mouse in Japan. 
BY 
Prof. C. Sasaki, Rigakuhakushi. 
Agricultural College, Imperial University, Tokyo, Japan. 
May ipoj. 
(With Plate IX.) 
Four years ago, field-mice made their appearance in the prefecture 
of Ibaraki lying north-east from Tokyo, and the injuries to crops extended 
not only over the whole prefecture, but also into the neighbouring provinces. 
In 1900, Dr. S. Onugi' and Mr. K. Sanui made some observations on their 
habits and have carried on their experiments for annihilating them by the 
inoculation of the so-called mouse typhusbacillus. In January 190 1, Dr. S. 
Onugi^ from a study of the characters of the mice and pointing out the dif- 
ferences between the latter and the house-rat, has concluded that the mice 
was probably of the same species with Arvicola subterraneous, Selys. In 
February of the same year, I also visited the above stated prefecture for the 
purpose of studying the characters and habits of the mice and made public 
my results in the Journal of the ^Agricultural Society of Japan, No. 235. 
In 1902, Prof Y. Kozai^ after two years' experiments for killing the 
mice by means of Mereskowsky's Bacillus, has obtained a satisfactorv result, 
and at present it is practically employed largely in various provinces. 
In the following lines, I will state the results of my studies upon the 
characters and habits of the hateful mice. 
Characters : Body rather small, but plump. Winter pelage : dorsally 
rusty greyish brown, ventrally greyish white (the dorsal hairs are greyish 
with rusty yellowish ends, while the ventral are greyish with whitish ends). 
There is no marked line laterally between the dorsal and ventral colora- 
tions. Tail rather short, covered sparsely with hairs, its dorsal hairs dark 
grey, and the ventral greyish white. Limbs light greyish brown. Snout 
1 Journal of the Agricultural society of Japan, No. 224, I goo. 
2 Ditio „ „ „ „ „ „ No. 233, 1901. 
5 The Bulletin of the College of Agriculture, Tokyo, Imp. Univ. Vol. IV. No. 5. 
