Towards the end of the age of the Old Red Sandstone or Devonian, a great
step in evolution was taken--the emergence of Amphibians. The earliest
representatives had fish-like characters even more marked than those
which may be discerned in the tadpoles of our frogs and toads, and there
is no doubt that amphibians sprang from a fish stock. But they made
great strides, associated in part with their attempts to get out of the
water on to dry land. From fossil forms we cannot say much in regard to
soft parts; but if we consider the living representatives of the class,
we may credit amphibians with such important acquisitions as fingers and
toes, a three-chambered heart, true ventral lungs, a drum to the ear, a
mobile tongue, and vocal cords. When animals began to be able to grasp
an object and when they began to be able to utter sufficient sounds, two
new doors were opened. Apart from insects, whose instrumental music had
probably begun before the end of the Devonian age, amphibians were the
first animals to have a voice. The primary meaning of this voice was
doubtless, as it is to-day in our frogs, a sex-call; but it was the
beginning of what was destined to play a very important part in the
evolution of the mind. In the course of ages the significance of the
voice broadened out; it became a parental call; it became an infant's
cry. Broadening still, it became a very useful means of recognition
among kindred, especially in the dark and in the intricacies of the
forest. Ages passed, and the voice rose on another turn of the
evolutionary spiral to be expressive of particular emotions beyond the
immediate circle of sex--emotions of joy and of fear, of jealousy and of
contentment. Finally, we judge, the animal--perhaps the bird was
first--began to give utterance to particular "words," indicative not
merely of emotions, but of particular things with an emotional halo,
such as "food," "enemy," "home." Long afterwards, words became _in man_
the medium of reasoned discourse. Sentences were made and judgments
expressed. But was not the beginning in the croaking of Amphibia?