290 THE CAUSES WHICH 



left lower ; and a specimen of the common Meadow Brown 

 Butterfly, taken near Oxford in 1878, showed the same transfor- 

 mation effected in the mider surfaces of the same wings, accom- 

 panied with the development of an additional vein and consequent 

 enlargement, that seemed to afford a reason how the hind wing 

 came to be folded so as to receive not alone the impress of the 

 inferior side, but the very eye-spot of the upper. The enlarge- 

 ment of spots and lines is evidently due to an excess of the 

 darker or lighter secretion as the case may be ; but how far the 

 dermal darkening, usually an indication of induration, may be 

 the result of exposure, it is in each case interesting to inquire. 

 Besides the wing patterns, the markings on the bodies of 

 Lepidoptera are likewise liable to chromatic variation. A speci- 

 men of the Clear Wing Trochilium culiciforme taken in Tilgate 

 Forest, for instance, had the usual red ring on the abdomen of 

 a white colour ; and from this cause likewise the gregarious 

 hammock-weaving Porthesia caterpillars, whose transformations 

 are synchronous, produce moths which closely approximate. 

 In colour, maybe, they slightly differ, as a milky from a 

 creamy white ; and the front wings of the male Gold Tail some- 

 times take four wing-flecks — two at the anal angle, one at the 

 apex, and rarely another just over the trifurcation of the central 

 vein — uncertain and hereditary features that will also at times 

 spring to light in its congener. But a main distinction has been 

 said to rest in the colour of the anal tuft and stain above on the 

 terminal portion of the hind body, that has originated the two 

 names which have the sanction of usage. In the Brown Tail 

 this stain is more or less marked and is of an umber colour, and 

 these hairs vary from a vandyke brown to a light and glossy 

 auburn. In the Gold Tail, where the stain is mostly seen in the 

 males, the tuft should be yellow, but it is not the less sometimes 

 of a deep brown colour fringed merely with a flaxen rim, leaving 

 it somewhat difficult to say which is the Gold Tail and which is 

 the Brown Tail species. 



A darkening in the colouration of our English ground beetles 

 may be observed as we go northward, connected, it has been sup- 

 posed, with a constitution better fitted to encounter unfavourable 

 conditions of life. Thus the common PterosticJius nigrita has 

 been found dwarfed with narrower and duller elytra; the little 



