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an extensive continent ; and, since tlie insects which at 

 present inhabit our earth must, if the doctrine of specific 

 centres be true, have been originally created in certaia 

 definite spots, let us suppose a limited proportion of 

 them to have been first produced upon this tract. Self- 

 dissemination, we will assimie, has been going on for 

 centuries : those species which were gifted with quick 

 diffusive powers have become pretty evenly dispersed 

 over its surface ; whilst those of naturally slow or seden- 

 tary habits have peopled, comparatively, but small areas 

 around the respective localities of their birth. Such may 

 have been the case, at some fixed period, amongst the 

 aborigiual beings of any country which we choose to 

 select as an illustration. But there is another element 

 to be considered. If this region be not insular, it wiU 

 have received colonists from foci of radiation situated 

 beyond its bounds; and these, therefore, according to 

 their several capabilities for progression, will have, like- 

 wise, in parts, overspread, or tenanted, it. Now it is 

 impossible to cite a more simple example than this. 

 But let us endeavour to realize what would be the neces- 

 sary consequence of the breaking up of such a district as 

 that which we have imagined. If a general sinking should 

 take place, causing its higher points to be alone visible 

 above the ocean, or merely ^partial one, so as to admit of 

 the sea encompassing portions of it which would remain 

 nnafiected in their altitude; the result practically would be 

 the same, — namely, the constitution of a group of islands 

 out of a once continuous land. Then, as regards the 



