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Ptinus albopictus, Woll. ; and it is so eminently a case 

 in pointj that it may be admissible to quote^ in extenso, 

 a few of the observations which I have already pub- 

 lished concerning it : — 



" The P. albopictus is the commonest of the Madeiran 

 Ptini, and by far the most variable, having a separate 

 radiatiag-form for almost every island of the group, — 

 whilst, at the same time, the whole are so intimately 

 connected together (and merge into each other) by 

 innumerable intermediate links, that it is impossible to 

 regard them, in spite of the opposite contour of the 

 extremes, in any other light than as different aspects of 

 a single species, according as circumstances may favour, 

 retard, or otherwise regulate its development. Insta- 

 bility in fact (in its broadest sense) may be considered 

 to be one of its most prominent characteristics, since it 

 appears to be more sensitive to isolation and altitude 

 than any of the other members of the genus with which 

 we have here to do,— as may be proved to a demonstra- 

 tion by a careful study of its habits on the spot, where 

 the influences of position and exposxire are, ia nearly all 

 instances, more than sufficient to account for the suc- 

 cessive phases assumed. Thus, commencing with var. a, 

 which reaches its maximum in the sheltered ravines of 

 the central mass, the bulk is usually large, and the tints 

 comparatively intense. Var. /3. is likewise brightly 

 variegated, but it is smaller. Now, if our premises be 

 correct, that locality and the action of the external 

 elements have much to do with the changes in question, 



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