in part through compensation of growth,
the effects of use, or of natural selection.

The development of the mammary glands would have been of no service, and
could not have been affected through natural selection, unless the young
at the same time were able to partake of the secretion. There is no
greater difficulty in understanding how young mammals have instinctively
learned to suck the breast, than in understanding how unhatched chickens
have learned to break the egg-shell by tapping against it with their
specially adapted beaks; or how a few hours after leaving the shell they
have learned to pick up grains of food. In such cases the most probable
solution seems to be, that the habit was at first acquired by practice
at a more advanced age, and afterwards transmitted to the offspring
at an earlier age. But the young kangaroo is said not to suck, only to
cling to the nipple of its mother, who has the power of injecting milk
into the mouth of her helpless, half-formed offspring. On this head
Mr. Mivart remarks: "Did no special provision exist, the young one must
infallibly be choked by the intrusion of the milk into the wind-pipe.
But there IS a special provision. The larynx is so elongated that
it rises up into the posterior end of the nasal passage, and is thus
enabled to give free entrance to the air for the lungs, while the milk
passes harmlessly on each side of this elongated larynx, and so safely
attains the gullet behind it." Mr. Mivart then asks how did natural
selection remove in the adult kangaroo (and in most other mammals, on
the assumption that they are descended from a marsupial form), "this at
least perfectly innocent and harmless structure?" It may be suggested
in answer that the voice, which is certainly of high importance to many
animals, could hardly have been used with full force as long as the
larynx entered the nasal passage; and Professor Flower has suggested
to me that this structure would have greatly interfered with an animal
swallowing solid food.

We will now turn for a short space to the lower divisions of the
animal kingdom. The Echinodermata (star-fishes, sea-urchins, etc.) are
furnished with remarkable organs, called pedicellariae, which consist,
when well developed, of a tridactyle forceps--that is, of one formed of
three serrated arms, neatly fitting together and placed on the summit of
a flexible stem, moved by muscles. These forceps can seize firmly hold
of any object; and Alexand