That
several of the inhabitants of the caves of the Old and New Worlds should
be closely related, we might expect from the well-known relationship
of most of their other productions. As a blind species of Bathyscia is
found in abundance on shady rocks far from caves, the loss of vision in
the cave species of this one genus has probably had no relation to its
dark habitation; for it is natural that an insect already deprived of
vision should readily become adapted to dark caverns. Another blind
genus (Anophthalmus) offers this remarkable peculiarity, that the
species, as Mr. Murray observes, have not as yet been found anywhere
except in caves; yet those which inhabit the several caves of Europe and
America are distinct; but it is possible that the progenitors of these
several species, while they were furnished with eyes, may formerly have
ranged over both continents, and then have become extinct, excepting in
their present secluded abodes. Far from feeling surprise that some of
the cave-animals should be very anomalous, as Agassiz has remarked in
regard to the blind fish, the Amblyopsis, and as is the case with the
blind Proteus, with reference to the reptiles of Europe, I am only
surprised that more wrecks of ancient life have not been preserved,
owing to the less severe competition to which the scanty inhabitants of
these dark abodes will have been exposed.

ACCLIMATISATION.

Habit is hereditary with plants, as in the period of flowering, in the
time of sleep, in the amount of rain requisite for seeds to germinate,
etc., and this leads me to say a few words on acclimatisation. As it
is extremely common for distinct species belonging to the same genus to
inhabit hot and cold countries, if it be true that all the species of
the same genus are descended from a single parent-form, acclimatisation
must be readily effected during a long course of descent. It is
notorious that each species is adapted to the climate of its own home:
species from an arctic or even from a temperate region cannot endure a
tropical climate, or conversely. So again, many succulent plants cannot
endure a damp climate. But the degree of adaptation of species to the
climates under which they live is often overrated. We may infer this
from our frequent inability to predict whether or not an imported plant
will endure our climate, and from the number of plants and animals
brought from different countries which are here perfectly healthy. We
have reaso