LAWS OF VARIATION 199 



this one genus has probably had no relation to its dark 

 habitation; for it is natural that an insect already de- 

 prived 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 surpj-ise 

 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 sur- 

 prised 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. 



A cclimatiza tion 



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 acclimatization. As it is ex- 

 tremely 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 

 rom a single parent form, acclimatization must be readily 

 sfiEected during a long course of descent. It is notorious 

 ;hat each species is adapted to the climate of its own 

 tiome: species from an arctic or even from a temperate 



