22 GEOTE — SPECIALIZATIONS OF LEPIDOPTEEOUS WING. [Jan. 21, 



originally a longitudinal vein rooting in base of wing and, as in 

 the Limnadidae, appears more as a ^pporting strap. However, in 

 Terias, where it is reduced, it assumes nearly the loop-like shape. 

 The minute study of this vein is a matter of some difficulty. The 

 appearance of vein viii in the Hesperiadae corresponds essentially 

 with that in the Sphingidae and Saturniades, where it has the loop- 

 like shape. These quaiititative changes are probably correlated 

 with mechanical function. On the secondaries of the Pieridae, 

 there are but slight differences in the amount of absorption of veins 

 ii and iii at base ; on the whole, the absorption is small and herein 

 is the wing generalized. Vein i, the so-called ''prascostal spur,'^ 

 is usually present ; it vanishes in the Eurymini and in Colias 

 (Gonepteryx); it may be seen in Callidryas. There is no equality 

 of specialization, no exact and equal step in all these instances and 

 the position of a genus or group can here not be assigned with cer- 

 tainty from any one character. Better, as a guide, is the radial 

 specialization on primaries^ where it may be laid down as an axiom 

 that the five-branched forms cannot possibly have been derived 

 from the three or four-branched, and that they are consequently 

 descendants of older types and clearly more generalized insects. 

 But neither may we group all the three or four-branched species to- 

 gether, since these specializations are reached upon what are other- 

 wise evidently independent phylogenetic lines, in all cases neces- 

 sarily succeeding a five-branched ancestor. Thus the three-branched 

 Pontia is clearly an offspring from the five-branched Anthocharini ; 

 the three-branched Nathalis is more immediately connected with 

 the four-branched Terias and Eurema. 



LeptidiancB. — So different is this butterfly and so isolated its 

 present position, that we must almost leave it out of sight in dis- 

 cussing the specialization of the Whites. The suppression of the 

 media is nearly limited to the extinction of the basal portion. 

 The position of vein ivo is central, or very nearly so, on fore wings, 

 cubital on hind wings; we have here an exceptional parallelism 

 with Papilio. The radius is generalized, five-branched. No trace 

 of vein viii appears on fore win^s. The median cells are small, re- 

 treating; the veins long. In comparison with the other whites, 

 the wings are in a generalized state, but the chances are that in 

 Leptidia (Leucophasia) we have a survival of what was a more 

 extended group at one period and that the generalization is strictly 

 relative. The disappearance of vein viii points in this direction. 



