They are very prolific, the female producing several litters in the year, each consisting of over a dozen blind young; and these, when not more than three weeks old, are turned out of the parental burrow to form underground homes for themselves.
In the month of the " diminishing of waters " the rain gods or Tlalocs were propitiated by a procession of priests with music of flutes and trumpets carrying on plumed litters infants with painted faces, in gay clothing with coloured paper wings, to be sacrificed on the mountains or in a whirlpool in the lake.
The experiments of the latter author show that, if a gametically pure black rat be crossed with an albino derived from a piebald black and white ancestry, all the offspring in successive litters will be black; but if the same black parent be crossed with albinoes extracted from parents of which one or both are grey, then both grey and black members will appear in the successive litters.
The female hits during the summer three or four litters, each of from two to seven young.
The nest is placed in clefts of rocks, among timber or in hollow trees, and there are generally three litters in a season.