are very closely allied to those of the surrounding
country. It would be most difficult to give any rational explanation of
the affinities of the blind cave-animals to the other inhabitants of the
two continents on the ordinary view of their independent creation. 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. Far from feeling any 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 inhabitants of these
dark abodes will probably have been exposed.

ACCLIMATISATION.

Habit is hereditary with plants, as in the period of flowering, in the
amount of rain requisite for seeds to germinate, in the time of sleep,
etc., and this leads me to say a few words on acclimatisation. As it is
extremely common for species of the same genus to inhabit very hot and
very cold countries, and as I believe that all the species of the same
genus have descended from a single parent, if this view be correct,
acclimatisation must be readily effected during long-continued 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 warmer countries which here enjoy good health.
We have reason to believe that species in a state of nature are limited
in their ranges by the competition of other organic beings quite as much
as, or more than, by adaptation to particular climates. But whether or
not the adaptation be generally very close, we have evidence, in
the case of some few plants, of their becoming, to a certain
extent, naturally habituated to different temperatures, or becoming
acclimatised: thus the pines and rhododendrons, raised from seed
collected by Dr. Hooker from tree