1889.] 177 



same in all individuals, and that if, in those cases where vein 7 is forked, we were 

 to suppose that it had become forked by division of its substance, or by budding, we 

 should be compelled also to assume that by some mysterious coincidence vein 8 dis- 

 appeared in precisely the same cases : whereas, the evident interpretation is that 

 vein 8 is itself transformed, by partial fusion, into a branch of 7. 



(5). Is simplification, or elaboration, to be regarded as pi-ogress ? Both con- 

 stantly take place, and theoretically either is equally likely to be advantageous ; the 

 direction of change is decided by so nice a balance of opposing circumstances, that 

 we are in general unable to point out why a particular change is profitable. Of 

 course Darwin has discussed this at full length. 



Finally, it may perhaps be useful if I indicate the various changes 

 which may take place in neural structure, as follows : — 



(a). Obsolescence : a vein may lose its normal tubular structure, 

 becoming attenuated and reduced in substance, until it appears a mere 

 fold of the membrane. Ex. : vein 5 of the hind-wings in Boarmia. 



(b). Stalking: two veins may be fused together for a portion of 

 their length from their base, so as to appear to rise on a common 

 stalk. Ex. : veins 8 and 9 of the fore-wings in all European Pyrales. 



(c). Coincidence: two veins may be fused together for the whole 

 of their length, so that one appears entirely absent ; this is really an 

 extreme form of stalking. Ex. : veins 10 and 11 of the fore-wings in 

 Urapteryx. 



(d). Anastomosis : two veins may rise separate, meet and be fused 

 together for a certain distance, and then separate again. Ex. : veins 

 9 and 10, and also 10 and 11, of the fore-wings in Cidaria. This term 

 is improperly used by Lord "Walsingham for (b). 



(e). Concurrence : a vein may rise separate, run into another, and 

 not separate again ; this is an extreme form of anastomosis. Ex. : 

 veins 11 and 12 of the fore- wings of Abraxas. 



if). Connection: two veins may be connected by a short trans- 

 verse bar passing from one to the other ; this is a rather curious form 

 of anastomosis, and is evolved from the ordinary form under the 

 influence of a tendency to lateral extension. This structure is un- 

 common, and I do not remember a pronounced instance among English 

 species ; but I have described some very well-marked cases among 

 exotic Geometrina. 



All other changes may be included under the head of modifications 

 in the direction or position of the simple veins. 

 Ramsbury : December 3rd, 1888. 



[Having had, in the course of my studies in Neuroptera, to deal very largely 

 with neuration, and other structural characters, I long ago came to the conclusion 



