which were secured alive and were probably at least a week old when
taken. This must have been exceptionally early for young, since of a
number of adult kangaroo rats taken during the first week of January
none have been found to be breeding. Two records from Vernon Bailey are
as follows: May 19-June 8, 1903, young specimen in nest (Santa Rosa, N.
Mex.); June 12, 1889, one female, two embryos (Oracle, Ariz.).

The considerable proportion (which we believe to be more than 50 per
cent) of nonbreeding females taken during all those months in which
breeding has been found to occur may also indicate an extended period of
breeding, with a small percentage breeding at any one time. This period
also furnishes ample time for the rearing of two litters a year by some
females, but we have no evidence as to the occurrence of two litters.
Young of the year, practically grown, are taken during and after the
month of April.

The mammae are arranged in three pairs, pectoral, 1/1; inguinal, 2/2.

Kangaroo rats are among those rodents in which the vagina becomes
plugged with a rather solid material, translucent, and of the
consistency of a stiff gelatine, after copulation. This must occur very
soon after coitus, since in those individuals taken in this condition no
definite evidence of the beginning of development of embryos could be
detected by examination.

The length of the gestation period of _spectabilis_ is unknown. The
young are born naked, a fact inferred by failure to find any fetus
showing noticeable hair development, and from the conditions observed in
such young as have been seen. A suckling female was taken by Vorhies,
January 31, 1920, and her den immediately excavated in the hope of