EFFECTS OF USE AND DISUSE. 125 



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 surrounding country. It 

 would be 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 inde- 

 pendent creation. That several cf 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. As a blind species of Bathyscia 

 is found in abundance on shadv rocks far from caves, the 

 losvj 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 dis- 

 tinct ; 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 ex- 

 tinct, 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 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 competition to which 

 the scanty inhabitants of these dark abodes will have been 

 exposed. 



ACCLIMATIZATION. 



Habit is hereditary with plants, as in the period ef 

 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 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, acclimntizHtion must be readily effected dur- 

 ing a long course of descent, it is notorious ihat eacb 



