152 ORIGIN OF SPECIES 



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 remark- 

 able 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, whilst 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 re- 

 gard 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 com- 

 petition to which the scanty inhabitants of these dark abodes 

 will have been exposed. 



ACCLIMATISATION 



Habit is hereditary with plants, as in the period of flower- 

 ing, in the time of sleep, in the amount of rain requisite for 

 seeds to germinate, &c., 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, accli- 

 matisation 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 con- 

 versely. 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 rea- 

 son to believe that species in a state of nature are closely 



