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eggs. Numerous Lamellicorn and Heteromerous insects,
the latter remarkable for their deeply sculptured bodies, were
slowly crawling about; while the Saurian tribe, the constant
inhabitants of a sandy soil, darted 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°; and in the middle of
the day the thermometer seldom ranged above 55°. On the
eleven succeeding days, in which all living things became so
animated, the mean was 58°, and the range in the middle of
the day between sixty and seventy. 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 Arideo, 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 5 8 °.4 ; the mean hottest day being 65°.5,
and the coldest 46°. The lowest point to which the thermometer
fell was 41°.5, and occasionally in the middle of the
day it rose to 69° or 7 0 °. A’et with this elevated 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 to the 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 required degree of
stimulus is adapted to the general climate of the place, and
how little it depends on absolute temperature. It is well
known that within the tropics, the hybernation, or more properly
estivation, of animals is governed 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 changed into pools of water by the rain, they were
peopled by numerous full-grown shells and beetles. 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 caU 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 allied
to A^’irgularia,* 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. It varies 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, which is separated into two
compartments; and in these, small, yellow, spherical ova are
contained. The stony axis which gives strength to the stem,
may be traced at this extremity into a mere vessel filled with
granular matter. This undeveloped portion is enclosed in a
transparent, elastic, irritable bag, containing a fluid in which
a very distmct circulation of particles could be seen. This bag
floats in one of the compartments of the fleshy terminal appendage.
At low water hundreds of these zoophytes might be
seen, projecting like stubble, with the truncate end upwards,
a few inches above the surface of the muddy sand. AAffien
touched or pulled, they drew themselves in, suddenly and
with force, so as nearly or quite to disappear. By this
action, the highly elastic axis must be bent at the lower
extremity, where it is naturally slightly curved; and I
imagine it is by this elasticity that the zoophyte is enabled
to rise again through the mud. Each polypus, though
closely united to its brethren, has a distinct mouth, body, and
tentacula. Of these polypi, in a large specimen, there must be
many thousands; yet we see that they act by one movement;
that they have one central axis connected with a system of
obscure circulation; and that the ova are produced in an
organ distinct from the separate individuals. AVell may one
be allowed to ask, what is an individual ? I will add only one
other observation on this zoophyte. The cavities leading
from the fleshy compartments of the extremity, were filled
1 b e liev e Virgidaria Patagónica oí' D ’O rb ig n y .
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