65 



to, and in those which have overspread (from without) 

 certain regions or localities, it is impossible not to asso- 

 ciate some inherent controlling power with the regions 

 themselves ; and we are driven to the conclusion, that 

 either well-defined races have been gradually shaped out, 

 by means of the physical influences to which they have 

 been exposed, or else that the species themselves (as 

 witnessed by the intermediate geographical links, which, 

 although sometimes rare, are in all instances to be found) 

 do assuredly merge into each other. 



In addition to those which we have been just discuss- 

 ing, there are other influences (equally independent of 

 mere heat and cold) by which insect modifications may 

 be brought about, modifications moreover of that pre- 

 cise character which must be referred, in general terms, 

 to the nature of the country and of the soil in which 

 they severally obtain : a very few examples, however, in 

 illustration of their action, must suffice for our present 

 purpose. The Tarus lineatus, Schb'iih., is slightly shorter 

 in Madeira, as also somewhat darker on its head and 

 prothoracic disk (and with its elytral strise less deeply 

 impressed), than it is in Algeria and Spain. The 

 Madeiran specimens of the Aphodius nitidulus, Fabr., 

 are usually a little paler, and more distinctly punctu- 

 lated, than their northern analogues; as are also, in 

 the latter respect, those of the Clypeaster pusillus, Gyll. 

 The Scydmcenus Helferi, Schaum, is permanently smaller 

 in the Madeiran group than it is in Sicily; and I 

 believe that the Achenium Hartungii, Heer, of those 



