1898] CLASSIFICATION OF THE DAY BUTTERFLIES 89 



and their branches : radius, media, cubitus. But the media is 

 now in a state of flux, of gradual wearing out, a process which 

 culminates in genera like Nymphalis, Naias, Fotamis^ Boihschildia, 

 Samia, Philosamia, Aitacus, wliere the media ceases to exist as a 

 distinct system ; (2) Subprinmry veins, longitudinal nervures lying 

 between the radius and costal edge of the wing (subcostal and costal 

 veins), and again between the cubitus and internal margin (veins 

 VI., VII., etc.). Veins II. (subcostal) and VII. on the forewings 

 are constant in all lepidoptera I have yet examined ; but, on hind- 

 wings, VII. is sometimes shortened, tending to obliteration as in 

 Parnassius ; VI. has almost everywhere practically passed away. 

 The condition which VII. displays in Parnassius shows us how VIII. 

 has been gradually got rid of in the Papilionides. 



Variation occurs sparingly with the movable veins within the 

 limit of the same species. Here these veins feebly take the same 

 course in variation which I have observed taking place as between 

 different species and higher assemblages of forms. These variations 

 •do not affect the general stability of the wing pattern ; they seem 

 •corroborative of the view of the general direction of the changes 

 which I have worked out. They also sustain a view that the 

 •differences we remark are quantitative rather than qualitative. 

 Aberrational stumps of veins may be also found; their unexpected 

 presence being perhaps owing to excess of nutriment or to mechani- 

 -cal, irritational causes. Again, rarely, a normally occurring vein 

 will suddenly cease, probably owing to defective tissue. 



To guide the student of the neuration, we have laid down the 

 following axiom: The extent of the absorption is every- 

 where the measure of the specialisation. 



jSTow, taking the venation of all the forms of the day butterflies 

 together, and comparing them, we find only one character which 

 allows of an apparently sharp dichotomy. This is presented by the 

 short, spur-like, stout vein which runs from the base of the wing in 

 the Papilionides and, in stronger or gentler curve, meets the internal 

 margin, not far from the base of the forewings. This character dis- 

 tinguishes the Parnassiidae and Papilionidae from all the other day 

 butterflies, including the Hesperiadae. This vein belongs to the sub- 

 stationary series of independent unbranched veins, which vanish by 

 disintegration and connect with the base of the wing. The 

 characters we get from it are therefore of subprimary value. 



We make here our first main division of the mass of the day 

 butterflies, and, before we go on any further, we must take up the 



^ Throughout this paper I use generic names as designating a specific type which has 

 been ascertained by historical methods and published in entomological literature. My 

 principal authority in the day butterHies for the correct use of generic titles is Mr 

 Scudder's "Historical Sketch," etc., Salem, 1875, a useful work which should be brought 

 'up to date and reprinted. 



G 



