September 7th, 1832, we thought nature had granted scarcely a living
creature to this sandy and dry country. By digging, however, in the
ground, several insects, large spiders, and lizards were found in a
half-torpid state. On the 15th, a few animals began to appear, and by
the 18th (three days from the equinox), everything announced the
commencement of spring. The plains were ornamented by the flowers of a
pink wood-sorrel, wild peas, cenotherae, and geraniums; and the birds
began to lay their eggs. Numerous Lamellicorn and Heteromerous
insects, the latter remarkable for their deeply sculptured bodies, were
slowly crawling about; while the lizard tribe, the constant inhabitants
of a sandy soil, darted about in every direction. During the first
eleven days, whilst nature was dormant, the mean temperature taken from
observations made every two hours on board the Beagle, was 51 degs.;
and in the middle of the day the thermometer seldom ranged above 55
degs. On the eleven succeeding days, in which all living things became
so animated, the mean was 58 degs., and the range in the middle of the
day between 60 and 70 degs. Here, then, an increase of seven degrees
in mean temperature, but a greater one of extreme heat, was sufficient
to awake the functions of life. At Monte Video, from which we had just
before sailed, in the twenty-three days included between the 26th of
July and the 19th of August, the mean temperature from 276 observations
was 58.4 degs.; the mean hottest day being 65.5 degs., and the coldest
46 degs. The lowest point to which the thermometer fell was 41.5
degs., and occasionally in the middle of the day it rose to 69 or 70
degs. Yet with this high temperature, almost every beetle, several
genera of spiders, snails, and land-shells, toads and lizards were all
lying torpid beneath stones. But we have seen that at Bahia Blanca,
which is four degrees southward and therefore with a climate only a
very little colder, this same temperature with a rather less extreme
heat, was sufficient to awake all orders of animated beings. This shows
how nicely the stimulus required to arouse hybernating animals is
governed by the usual climate of the district, and not by the absolute
heat. It is well known that within the tropics, the hybernation, or
more properly aestivation, of animals is determined not by the
temperature, but by the times of drought. Near Rio de Janeiro, I was
at first surprised to observe, that, a few days after some little
depressions had been filled with water, they were peopled by numerous
full-grown shells and beetles, which must have been lying dormant.
Humboldt has related the strange accident of a hovel having been
erected over a spot where a young crocodile lay buried in the hardened
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