During The Remainder Of My Stay At Rio, I Resided In A
Cottage At Botofogo Bay.
It was impossible to wish for
anything more delightful than thus to spend some weeks
in so magnificent a country.
In England any person fond
of natural history enjoys in his walks a great advantage, by
always having something to attract his attention; but in
these fertile climates, teeming with life, the attractions are
so numerous, that he is scarcely able to walk at all.
The few observations which I was enabled to make were
almost exclusively confined to the invertebrate animals. The
existence of a division of the genus Planaria, which inhabits
the dry land, interested me much. These animals are of so
simple a structure, that Cuvier has arranged them with the
intestinal worms, though never found within the bodies of
other animals. Numerous species inhabit both salt and fresh
water; but those to which I allude were found, even in the
drier parts of the forest, beneath logs of rotten wood, on
which I believe they feed. In general form they resemble
little slugs, but are very much narrower in proportion, and
several of the species are beautifully coloured with
longitudinal stripes. Their structure is very simple: near the
middle of the under or crawling surface there are two small
transverse slits, from the anterior one of which a funnel-
shaped and highly irritable mouth can be protruded. For
some time after the rest of the animal was completely dead
from the effects of salt water or any other cause, this organ
still retained its vitality.
I found no less than twelve different species of terrestrial
Planariae in different parts of the southern hemisphere. [3]
Some specimens which I obtained at Van Dieman's Land,
I kept alive for nearly two months, feeding them on rotten
wood. Having cut one of them transversely into two nearly
equal parts, in the course of a fortnight both had the shape
of perfect animals. I had, however, so divided the body,
that one of the halves contained both the inferior orifices,
and the other, in consequence, none. In the course of twenty-
five days from the operation, the more perfect half could
not have been distinguished from any other specimen. The
other had increased much in size; and towards its posterior
end, a clear space was formed in the parenchymatous mass,
in which a rudimentary cup-shaped mouth could clearly be
distinguished; on the under surface, however, no corresponding
slit was yet open. If the increased heat of the weather,
as we approached the equator, had not destroyed all the
individuals, there can be no doubt that this last step would
have completed its structure. Although so well-known an
experiment, it was interesting to watch the gradual production
of every essential organ, out of the simple extremity
of another animal. It is extremely difficult to preserve these
Planariae; as soon as the cessation of life allows the ordinary
laws of change to act, their entire bodies become soft
and fluid, with a rapidity which I have never seen equalled.
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