The Outline of Science, Vol. 1 (of 4): A Plain Story Simply ToldThomson, J. Arthur (John Arthur)
Science
The Outline of Science, Vol. 1 (of 4): A Plain Story Simply Told
Thomson, J. Arthur (John Arthur)
Science
As Amphibians had their Golden Age in the Carboniferous period we may
fitly use this opportunity of indicating the advances in evolution which
the emergence of Amphibians implied. (1) In the first place the passage
from water to dry land was the beginning of a higher and more promiseful
life, taxed no doubt by increased difficulties. The natural question
rises why animals should have migrated from water to dry land at all
when great difficulties were involved in the transition. The answers
must be: (_a_) that local drying up of water-basins or elevations of the
land surface often made the old haunts untenable; (_b_) that there may
have been great congestion and competition in the old quarters; and
(_c_) that there has been an undeniable endeavour after well-being
throughout the history of animal life. In the same way with mankind,
migrations were prompted by the setting in of prolonged drought, by
over-population, and by the spirit of adventure. (2) In Amphibians for
the first time the non-digitate paired fins of fishes were replaced by
limbs with fingers and toes. This implied an advantageous power of
grasping, of holding firm, of putting food into the mouth, of feeling
things in three dimensions. (3) We cannot be positive in regard to the
soft parts of the ancient Amphibians known only as fossils, but if they
were in a general way like the frogs and toads, newts and salamanders of
the present day, we may say that they made among other acquisitions the
following: true ventral lungs, a three-chambered heart, a movable
tongue, a drum to the ear, and lids to the eyes. It is very interesting
to find that though the tongue of the tadpole has some muscle-fibres in
it, they are not strong enough to effect movement, recalling the tongue
of fishes, which has not any muscles at all. Gradually, as the tadpole
becomes a frog, the muscle-fibres grow in strength, and make it possible
for the full-grown creature to shoot out its tongue upon insects. This
is probably a recapitulation of what was accomplished in the course of
millennia in the history of the Amphibian race. (4) Another acquisition
made by Amphibians was a voice, due, as in ourselves, to the rapid
passage of air over taut membranes (vocal cords) stretched in the
larynx. It is an interesting fact that for millions of years there was
upon the earth no sound of life at all, only the noise of wind and wave,
thunder and avalanche. Apart from the instrumental music of some
insects, perhaps beginning in the Carboniferous, the first vital sounds
were due to Amphibians, and theirs certainly was the first voice--surely
one of the great steps in organic evolution.
[Illustration: _Photo: British Museum (Natural History)._
FOSSIL OF A PTERODACTYL OR EXTINCT FLYING DRAGON
Public-domain text, read in full here on John Shaqi.
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