BULLETIN FLORIDA STATE MUSEUM VOL 34(6)


et al. 1959; Hanney 1965; Coetzee 1965; Delany and Neal 1969). These other
averages, however, are based upon far fewer females examined: in the one
study where the number of P. natalensis was adequate (4636, Coetzee 1965),
only 481 females were dissected. Coetzee (1967) reported data on intrauterine
mortality thus: corpora lutea averaged 10.92, 9.47 embryos were implanted,
and 9.22 healthy fetuses were observed. In the present study, the average of
12.2 embryos less than 10 mm decreased to 11.8 between 10 mm and 19 mm,
and 10.6 in excess of 19 mm. Coetzee's (1965) average litter size of 9.5 may
indicate a slight difference in reproductive rate between South Africa and
Tanzania, or could indicate that the two populations are not conspecific.
 Coetzee (1975) reported a low breeding rate during dry season (winter),
with a break in reproduction in September, while Delany and Neal (1969)
found reproductive females in Uganda from May to July and October to
December, commenting that "peak breeding season occurs mainly towards the
end of the rainy season and beginning of the dry season." Their samples were
taken from sites between 900 m and 1100 m elevation, where some rainfall
appears to occur in every month. In Malawi, Hanney (1965) examined 159
female P. natalensis without finding pregnant females from June to January.
Hubbard (1972) presented fragmentary data from an overall sample of 225
females taken in several Tanzanian localities (Muheza, Lake Manyara, Iringa,
Njombe, and Himo), reporting pregnant females in January, February, March,
May, July, September, and November, but the data are virtually meaningless
given the variety of rainfall patterns which occur over that broad area.
 Some of the observations by Harris (1937) were based upon material
from Morogoro; He described P. natalensis as being least active from January
to May, with "The majority of the mice at this time appear to be young and in
good condition." Maturation of both sexes occurred about the beginning of
March, followed soon by pregnant females and young, while maximum
numbers were found in July and August. Although Harris studied fluctuations
in numbers for two years at Morogoro, from December 1931 to December
1933, he apparently did not publish quantitative data from his work nor a
detailed description of methods, which unfortunately prevents a direct
comparison with the present study.
 The data of Chapman et al. (1959) from Rukwa in Mbeya Region are
based upon erratically collected material but, as presented by Coetzee (1975),
show a pattern of reproduction somewhat different to that found in Morogoro
during the present study. The percentage of juveniles in the population
reached maxima in May and June, remained high until October, then declined
rapidly through March, rising again from April. In Morogoro, the juvenile
cohort rose continuously relative to the adult component from July to
December of each year, as an overall pattern, though the rise began earlier in
1984 (April). The decrease in juvenile percentage found in Rukwa can be
attributed to possibly earlier maturation, beginning in October rather than


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