Chap. V. 
ACCLIMATISATIOIT. 
139 
Professor Dana; and some of the European cave- 
insects are very closely allied to those of the surround¬ 
ing 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 sur¬ 
prise that some of the cave-animals should be very 
anomalous, as Agassiz has remarked in regard to the 
blind ffish, 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 com¬ 
petition 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 requi¬ 
site for seeds to germinate, in the time of sleep, &c., 
and this leads me to say a few words on acclimatisa¬ 
tion. 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. 
