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already insisted upon. Like most of the minutiae of 

 variation, however, to which we have called attention, it is 

 more particularly on islands that this is to be observed, 

 isolation, during an interval sufficiently long, appear- 

 ing to possess some especial control over the external 

 contour and surface of the insect races. Thus, in the 

 Madeiras, for instance, the Caulotropis lucifugus has its 

 prothorax more distinctly punctured, and its elytra more 

 perceptibly striated, in the principal island, than on any 

 of the smaller members of the group ; in Porto Santo, 

 indeed, it is almost free from sculpture of any kind ; 

 whilst its ally, the C. conicollis, apart from being some- 

 what larger, is, on the contrary, both more punctured 

 and striated on the Dezerta Grande than it is in Madeira 

 proper. The Omias Waterhousei, again (in addition to 

 its slightly increased bulk and less shining envelope, in 

 that locality), is more lightly impressed on the Dezerta 

 than it is in Madeira : and, not to mention other differ- 

 ences, the Ellipsodes glabratus is densely beset with 

 most minute granules on that same rock whereas on 

 the mountain slopes of the central mass, it is highly 

 polished and glabrous. The Helops confertus, we have 

 intimated at a previous page, is less coarsely sculptured 

 in the lofty regions of Madeira, than in the lower ones : 

 and the H. futilis has its elytral tubercles apparent in 

 Madeira proper, but evanescent on the Dezerta Grande. 

 The Eurygnathus Latreillei assumes a permanent variety 

 on the Dezerta, the insect having become modified 

 through a long isolation on those weather-beaten heights, 



