larger number
(McAtee, 1921, 258).

Much more information on enemies is needed. The relatively low rate of
reproduction (see p. 18) indicates comparative freedom from inimical
factors.

PARASITES.

_Dipodomys s. spectabilis_ is regularly infested with a species of flea,
_Ctenophthalmus_ sp. Seldom or never is a specimen taken in reasonably
fresh condition without some of these parasites present on its body,
though of course they desert the body of the host after it becomes cold,
and hence dead specimens left too long may be free from them. The den
conditions are ideal for the breeding of this parasite, because of the
great quantities of fine, dusty, organic refuse littering the tunnels
and furnishing food and refuge for the larvae. As demonstrated to us by
F. C. Bishopp, of the Bureau of Entomology, a handful of this refuse
taken from the floor of a burrow within arm's length of the entrance is
almost certain to contain these larvae.

Less regularly present, perhaps because of its different life history,
is a small tick, _Trombicula_ sp. At times this parasite is very common,
being present on nearly every individual rat, and at other times
specimens are difficult to find; it appears to be more commonly present
in summer and fall than at other seasons, and is found attached chiefly
to the ears.

No internal parasites have been detected. The nocturnal and fossorial
habits of the animal seem to give complete protection against a form of
parasite which is very common among some other rodents of the Range
Reserve, notably _Lepus_ and _Sylvilagus_. Nearly all rabbits are
infested with "warbles," the larvae of a species of bot-fly, _Cuterebra_
(family Oestridae). Other small mammals also are occasionally
parasitized by the _Cuterebra_, but in the handling and examination of
perhaps 200 or more individuals of _spectabilis_ and _merriami_, we have
yet to find a single case of infestation by an oestrid fly.

ABUNDANCE.

One's first impression of a well-occupied _spectabilis_ area is that a
large family must inhabit each den, but, as previously mentioned, we
have gradually been compelled to shift from this conception to the idea
of but a single animal to a mound, except when the young are present.
Therefore a census of the adult kangaroo rat population can readily be
made, simply by counting the mounds. Such a census affords at least a
conservative estimate of the number of adult individuals occupying a
given