104 ACCLIMATISATION. [CHAP. V. 



be closely related, we might expect from the well-known relation- 

 ship 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, 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 regard to the blind fish, the Ambly- 

 opsis, and as is the case with the blind Proteus with reference to 

 the reptiles of Eui'ope, 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, &c., and this leads me to say a few words on acclima- 

 tisation. 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 inf ?r 

 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 reason to believe that species 

 in a state of nature are closely 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 n$? 

 this adaptation is in most cases very close, we have evidence with 

 some few plants, of their becoming, to a certain extent, natur- 

 ally habituated to different temperatures; that is, they become 





