126 ON THE ORIGIN OF SPECIES 



ness.' By the time that an animal had reached, after 

 numberless generations, the deepest recesses, disuse 

 will on this view have more or less perfectly obliter- 

 ated its eyes, and natural selection will often have 

 effected other changes, such as an increase in the 

 length of the antenna or palpi, as a compensation 

 for blindness. Notwithstanding such modifications, 

 we might expect still to see in the cave-animals of 

 America, affinities to the other inhabitants of that 

 continent, and in those of Europe, to the inhabitants 

 of the European continent. And this is the case with 

 some of the American cave-animals, as I hear from 

 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 fife 

 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 

 requisite for seeds to germinate, in the time of sleep, 

 etc. , and this leads me to say a few words on acclima- 

 tisation. 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 



