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High and low Dimorphism. 



With an account of certain Tauaidae of the Bay of Naples. 



By 

 Geoffrey Smith, 



New College, Oxford. 



With Plates 20, 21 and 13fisures in the text. 



I. Introductiou. 



The oceurrence of high and low dimorphism has for long been 

 known to collectors of insects, and the pheuomenon is probably 

 familiär to anyoue who has seen a series of the males of the common 

 Stag beetle or iudeed of almost any beetle in which the sexes are 

 distinguished by well-marked structural differences. It consists 

 essentially in the existence among the males of any speeies of a 

 graduated series, as regards size and the development of the secon- 

 dary sexual charaeters, such tbat the smaller males bave relatively 

 poorly developed secondary sexual charaeters while the larger males 

 attain to a much greater relative development of those charaeters. 

 The smaller males are then termed "low", and the larger males 

 "high": when there is a more or less abrupt trausition in point of 

 numbers from high to low males we may most properly speak of 

 a high and low dimorphism existing in tbe males of that speeies, 

 but we also apply tlie term more loosely to those cases in which 

 no such abrupt transition is proved to occur. 



The object of the following pages is to extend the application 

 of this phenomenon to several new cases , to endeavour to trace it 

 to its causai connection in the general manifestation of the living 

 organism, and to indicate its hearing upon the i)roblem of organic 

 cbange. It has been found possible to trace the existence and in- 

 tìuence of the principio which uuderlies this phenomenon in very 



