16 MAMMALS

everywhere testifying to the infinity of its Author ;
never a living form transmitting its unaltered like-
ness to distant futurity, and yet nothing in the end
which was not also in the beginning. Truly a
wonderful world as it lies open to us, modelled and
moulded, as a whole and in its least molecule, with
grandeur, unfathomable intelligence, and inexhausti-
ble bounty.

During our lifetime our knowledge of animal life
in the present and the past has largely increased, and
the hard-and-fast frontier lines drawn by our fathers
have in many cases been wiped away, and in others
have been replaced by mere strips of debateable land.
Even among the greater divisions which seemed so
firmly established, many approximations have been
made out. The fishes, for instance, have been found
to be closely allied to the amphibians, the reptiles to
the birds, and even the vertebrates as a whole have
been shown to be so linked to the invertebrates that
zoologists are abandoning the backbone as a basis of
classification in favour of the spinal cord. Animals
are now sorted into chordates, hemi-chordates and so
on, and non-chordates ; the spinal cord in the chordates
being along the back, and the heart being ventral, while
the nerve cords of the non-chordates are along the
belly or the sides, the heart being dorsal; the inter-
mediate classes giving the intermediate stages in
which the animal forms appear to have gradually
turned upside down. On such technical details we
need not, however, dwell in this little book ; we have
merely mentioned them as illustrations of the ex-