If During A Warm
Day We Look Either At The Shadow Of Any Object Cast On A
Bank, Or Over
A level plain at a distant landmark, the effect
of an ascending current of heated air is almost always evident:
Such upward currents, it has been remarked, are also
shown by the ascent of soap-bubbles, which will not rise in
an in-doors room. Hence I think there is not much difficulty
in understanding the ascent of the fine lines projected from
a spider's spinners, and afterwards of the spider itself; the
divergence of the lines has been attempted to be explained, I
believe by Mr. Murray, by their similar electrical condition.
The circumstance of spiders of the same species, but of
different sexes and ages, being found on several occasions at
the distance of many leagues from the land, attached in vast
numbers to the lines, renders it probable that the habit of
sailing through the air is as characteristic of this tribe, as
that of diving is of the Argyroneta. We may then reject
Latreille's supposition, that the gossamer owes its origin
indifferently to the young of several genera of spiders:
although, as we have seen, the young of other spiders do
possess the power of performing aerial voyages. [7]
During our different passages south of the Plata, I often
towed astern a net made of bunting, and thus caught many
curious animals. Of Crustacea there were many strange
and undescribed genera. One, which in some respects is
allied to the Notopods (or those crabs which have their
posterior legs placed almost on their backs, for the purpose
of adhering to the under side of rocks), is very remarkable
from the structure of its hind pair of legs. The penultimate
joint, instead of terminating in a simple claw, ends in three
bristle-like appendages of dissimilar lengths - the longest
equalling that of the entire leg. These claws are very thin,
and are serrated with the finest teeth, directed backwards:
their curved extremities are flattened, and on this part five
most minute cups are placed which seem to act in the same
manner as the suckers on the arms of the cuttle-fish. As
the animal lives in the open sea, and probably wants a place
of rest, I suppose this beautiful and most anomalous structure
is adapted to take hold of floating marine animals.
In deep water, far from the land, the number of living
creatures is extremely small: south of the latitude 35 degs.,
I never succeeded in catching anything besides some beroe,
and a few species of minute entomostracous crustacea.
In shoaler water, at the distance of a few miles from the
coast, very many kinds of crustacea and some other animals
are numerous, but only during the night. Between latitudes
56 and 57 degs. south of Cape Horn, the net was put
astern several times; it never, however, brought up anything
besides a few of two extremely minute species of Entomostraca.
Yet whales and seals, petrels and albatross, are exceedingly
abundant throughout this part of the ocean.
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