SS NATURAL SCIENCE [February 



IX. Applied only by me to the more or less curved vein in the 

 Papilionides, running from base to internal margin. Whether this 

 is homologous with VIII., to which it is opposed in position, is un- 

 certain. 



HiNDWINGS 



The same system prevails, since the veins are homologous with 

 those on forewings. In Hepialus and Microptcryx the radius is 

 generalised and exhibits five branches. In all other lepidoptera, 

 except probably some Tineidae like C. familiella, the radius is 

 single-branched. Since the five-branched radius represents a 

 generalised condition, we infer that the primitive lepidoptera had a 

 five-branched radius on the hindwings and that the front and hind 

 pair of wings were in this feature alike, as is the case in Ifcpialus, 

 which we accordingly treat as a specialised survival of a once gene- 

 rally prevailing type. Most specialisation seems to be inaugurated 

 on the hindwings and we find, generally, that here the details of the 

 specialising movements are more clearly expressed. While the 

 same system of enumeration applies equally to the veins of the hind- 

 wings, the costal vein has a different expression from that on 

 primaries. The frenulum of the moths is a specialised bristle or 

 hair, not a vein ; while the original clothing of the lepidoptera seems 

 to have been hairy, the scales being probably a more recent 

 specialisation. The costal vein forms, on the hindwings of the 

 diurnal butterflies, a salient projection at base, where it generally 

 issues from vein II. Its evolution is shown by the Parnassi- 

 Papilionidae ; in Papilio it appears as a blunt separate process ; in 

 Thais its fusion at extreme base is partially, in Parnassius fully 

 accomplished. It is sometimes called the ' praecostal spur.' The 

 internal veins below VIL, probably originally parallel rods, usually 

 present but varying in number or in completeness, are sometimes all 

 wanting, as in the Papilionides and most of the Saturniades. Besides 

 these parallel veins there are a few cross-veins on both wings, con- 

 necting two parallel veins, as the intercostal vein in the hindwings 

 •of the Sphingides, and the vein connecting cubitus and vein VIII. 

 in the forewings of Papilio. According to my view, which is here 

 opposed to that of Professor Comstock, these are all, including the 

 usual cross-vein closing the medium cell outwardly, relics, perhaps 

 secondarily modified, of former systems of cross-veins, which have 

 partly disappeared with time. However, this conclusion is based on 

 analogy. But the question becomes important, because, under my 

 view, vein VL will have quite vanished in Papilio, while a former 

 cross-vein will have been here retained. 



The whole system of neuration, in respect to the posi- 

 tion of the veins, may be divided as follows: (1) Primary veins 



