296 THE CAUSES WHICH 



features in climatic variation,, and it is stated the common Mole 

 Cricket is not only smaller in Southern Europe, but that its fore 

 (jr digging legs are differently toothed. 



In conclusion, the discrimination of species and variety is most 

 feasible in butterflies and moths, where the specimens take decided 

 diversity of form in all their stages. On proceeding to consider 

 the beetles, we find their obscurer transformations less marked and 

 less studied, and in such cases general similarity, with obsei-va- 

 tion on habit and pairing of the sexes, becomes the sole specific 

 test. The same remarks apply as forcibly to those classes where 

 little differentiation is marked during development, as indeed to 

 the remaining orders inclusively, where there is very little to fix 

 what is species and what induced variety. Not that there can 

 be any doubt but that the laws of variation are in operation here 

 as elsewhere, and in rapacious dragon-flies pattern deviations 

 of the war-paint occur quite in consonance. Thus we have 

 a Scottish variety of the Four Spotted Libellula, and a local sort 

 with the extremities of the wing blackish. In Northern Italy 

 two others of these large flat-bodied species vary, one being our 

 common large Blue Dragon Fly, L. depressa ; and from Etruria 

 Rossi mentions a variety of the female of the equally common 

 Demoiselle, Caleoj^teryx Firffo,tha.t has black body and black wings. 

 Then Caleojpteryx Vesta, Charp., of our Epping Forest is likewise 

 considered a variety where the reddish wings of the male have 

 not acquired their bluish adult hue, though it also differs in 

 habit, being found far from water. As bright dragon-flies and 

 flies mostly acquire their body colours by the sun's action on the 

 pigment of the skin or dermis, the blue and red males on first 

 emerging assuming the sober tints of the females, on which by 

 transition their proper vice is branded, blue exudation being 

 preceded by feminine yellow or brown, red and carmine by 

 feminine yellow, orange, or olive ; it is quite palpable an arrest- 

 ing of this process must evoke parti-coloured varieties, and such 

 sorts are now and then met with at large. These few observa- 

 tions I extract from the Baron de Selys Longschamp's work on 

 " European Dragon Flies ; " and on turning to the other group 

 of Neuroptera containing the May Flies, I find a note by Mr. 

 M'Lachlan stating that those specimens of the Common Lace 

 Wing which have hibernated may be known by their reddish 



