Variation of litter sizes and correlation between litter size and number of mammae were studied on the following Japanese species:
Microtus montebelli, Clethrionomys rufocanus bedfordiae, Aschizomys niigatae, Eothenomys smithi and Eothenomys kageus.
The variations of litter sizes of those species are shown in table 1. The mammal formulae are always 2+0+2=8 in
montebelli, bedfordiae and
niigatae, 1+0+2=6 in
smithi and 0+0+2=4 in
kageus. Therefore the litter size (table 1) and number of mammae are evidently correlative in those species except
niigatae (r±PEr =0.739±0.051) .
Aschizomys niigatae which had been reffered to
Clethrionomys is quite different in litter size from
bedfordiae in spite of the same number in mamrnae.
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