ryos (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
securing the young. Two juveniles were found in a special nest chamber
(see p. 30). These were estimated to be perhaps two weeks old. A serious
effort was made to raise the little animals by feeding milk with a
pipette and keeping them warm with a hot water bottle, but they survived
only 10 days, without the eyes having opened. The uneven temperature as
well as the character of the food was probably responsible for their
deaths. On February 3 they were measured and weighed, with the following
results:

---------------------------------------------------
| | Measurements (in millimetres).
| Weight |-------------------------------
| (in | Total | Tail | Hind
| grams). | length. | vertebrae. | foot.
---------|---------|---------|------------|--------
No. 1 | 13.3 | 90 | 38 | 24
No. 2 | 12.6 | 93 | 38 | 24
---------------------------------------------------

At this stage the young were partially clothed with a coat of fine
velvety fur, more especially on the bodies, the tails being still nearly
naked. The body color was dark p