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 degrees; the mean
hottest day being 65.5 degrees, and the coldest 46 degrees. The
lowest point to which the thermometer fell was 41.5 degrees, and
occasionally in the middle of the day it rose to 69 or 70 degrees.
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 mud. He
adds, "The Indians often find enormous boas, which they call Uji,
or water serpents, in the same lethargic state. To reanimate them,
they must be irritated or wetted with water."

I will only mention one other animal, a zoophyte (I believe
Virgularia Patagonica), a kind of sea-pen. It consists of a thin,
straight, fleshy stem, with alternate rows of polypi on each side,
and surrounding an elastic stony axis, varying in length from eight
inches to two feet. The stem at one extremity is truncate, but at
the other is terminated by a vermiform fleshy appendage. The stony
axis which gives strength to the stem may be traced at this
extremity into a mere vessel filled with granular matter. At low
water hundreds of these zoophytes might be seen, projecting like
stubble, with the truncate end upwards, a few inches above the