Chap. V. ACCLIMATISATION. 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 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 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. 



