156 ■ f December, 



reasoned that the species is in a state of progressive development. 

 What is the direction of this development ? Which is the older or 

 more ancestral form ? Does the multiplication or complication of 

 wing veins, or the diminution of their numbers, and consequent sim- 

 plification of structure, constitute the improvement aimed at in 

 Nature ? When the apical vein is forked, is it to be considered that 

 the vein which should be separate and below it is partly anastomosed 

 with it, or that its tendency is to become reduplicated so as to provide 

 additional support to the delicate intervenal wing structure ? 



If we take C. alpella, G. vittella, and C. sylvella, we find their 

 structure to be — alpella C, vittella <, sylvella <, which of these is 

 the earlier form, and in what order should we place them? 



In a few rare instances the lower of the two veins is found bent 

 in the middle, as if endeavouring to approach the vein above it. I 

 have found this to occur in a specimen of C. scabrella and C. paren- 

 thesella — this certainly favours the theory of anastomosis ; moreover, 

 where the vein is forked, the stem of the H often presents under the 

 lens a reduplicated appearance, but it is difficult to comprehend what 

 constitutes the advantage to the species in such a reduction of the 

 number of wing-supports. Does simplicity of neuration conduce' to 

 strength, or would it not be more probable than an elaboration of 

 structure should be regarded as progressive development ? 



It should be noted that in the diagram which accompanies this 

 paper the form of neuration has been determined by touching the 

 wings with benzine, and carefully examining them under a strong 

 light. In doubtful cases the bases of the veins have frequently been 

 denuded with a camel's hair brush. It may be taken for granted that 

 in nearly all instances the form has been correctly determined, but the 

 length of stem in forked veins is extremely variable ; some are forked 

 towards the apex, others so near the base as to make it difficult to 

 decide whether the sign H or ^ should rightly be used ; the same 

 observation applies as between the signs <1 and c|, but great care has 

 been taken to avoid mistakes. 



Occasional monstrosities are met with in which the apical veins 

 are more or less distorted ; these are very scarce, and not mentioned 

 in the table given above. In one specimen of Trachoma scabrella a 

 small supplementary cell was found at the upper extremity of the 

 discal cell. 



Merton Hall, Thetford : 



October 22nd, 1888. 



