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reached what now constitute the various islands of the 

 cluster, we at once detect traces of this fact, through 

 their more or less altered aspects, the result of isola- 

 tion, and diminished range, during the enormous in- 

 terval which has elapsed since the successive* convulsions 

 which caused the partial destruction of this Atlantic 

 province were brought to a close. 



To return, however, to the insects, after this long con- 

 chological digression, I need not multiply evidence, in 

 corroboration of my theory. Enough has been said to 

 render intelligible the idea which I wished to convey, 

 concerning the general direction of the migratory current 

 over that ancient tract, and the extreme slowness of its 

 progress, the former of which I consider probable 

 from the north-easterly course in which creatures generi- 

 cally identical were, if we may so express it, " given- 

 off -" whilst the circumstance of their being for the 

 most part specifically dissimilar (or, in other words, of 

 the islands harbouring, many of them, species which 

 are endemic) would seem as it were to establish the 

 latter. 



We must not however forget, that it is only to the 

 aborigines of this quondam land that the above specula- 

 tions apply. Assuming the region not to have been 

 insular, that is to say, to have been connected, on its 

 outer limits, with a European, or Mediterranean, conti- 

 nent ; it would necessarily follow, that a certain number 

 of colonists must have found their way over its area, 

 and moreover in an opposite direction to the living 



