Abstract
From November of 1948 to April of 1949, the rat control was practised in the city of Sapporo by the use of ANTU, the poisonous diet, and 4171 dead specimens of the Norway rat (Rattus uorvegicus) were collected. We observed the occurrence among them of nine mutant individuals having aberrant coat colours.
They are as follows;
1) Black (non-agouti): Uniform black in coat colour (Fig. 1). _??_, March 29, 1949.
2) Dilute (?): Pigmentation extremely diminished, very pale brownish grey in colour (Fig. 2). _??_, Jan. 11, 1949.
3) Silver (?): Black coat interspersed with white hairs (Figs. 3-4). _??_ _??_, Nov. 27, 1948.
4) Albino (?): Uniform white in colour (Fig. 5). _??_ _??_ _??_ _??_, Dec. 1, 1948; March 1, 17; April 9, 1949.
5) Piebald (?): Appearance close to the piebald (hooded) mutant. _??_, Nov.15, 1948.
