262 MR. E. B. POULTON ON THE EXTERNAL 



moth project from the opening (see figure), so that the initial part of the process of emergence 

 is still preserved in this degenerate form. The comparison between pupa and imago confirms 

 the conclusion already arrived at, that the degeneration of female imagines of Lepidoptera is 

 comparatively recent in date. The male pupa of this species is well developed. 

 Fig. 16. x 7. The left pupal wings of Cynthia cardui. The hind wing (H.W.) is seen at two points 

 along the dorsal margin of the fore wing, which covers it elsewhere. Well within the hind 

 margin (H.M. ) of the pupal fore wing is seen a hind margin (H'.M'.) which corresponds to that 

 of the imaginal wing. It is clear that the imaginal wing is only developed over a part -of the 

 space enclosed by the pupal wing. Thus the venation extends up to the future imaginal hind 

 margin (H'.M'.), and there abruptly ceases (compare fig. 18), while the arrangement of the 

 pigment also undergoes abrupt modification at the same limits. Some traces of the alternation 

 of black and white which is so conspicuous in the fringe of the imaginal hind margin (fig. 17) 

 may also be detected in the disposition of the pigment along H'.M'. In this and the succeed- 

 ing figures of pupal wings, the cuticle was flattened as far as possible in order to facilitate the 

 drawing. 

 Pig. 17. Natural size. The outline of the left fore wing of the imago of Cynthia cardui, for comparison 

 with the last figure. The hind margin of the wing is seen closely to resemble the corresponding 

 line upon the pupa (H'.M'.), the only difference being that the bay is slightly deeper in the 

 imago. A smooth continuous hind margin is far commoner than a bayed or indented margin in 

 Lepidoptera, and is probably more ancestral. It appears therefore that, as in other structural 

 changes of recent date, the pupa presents us with an earlier stage of the process of modification. 

 Fig. 18. x 7. The left pupal wings of Vanessa Atalanta. The venation is remarkably distinct, and the 

 parts which are represented correspond precisely with that of the imaginal wing. This is all 

 the more remarkable because the tracheae of the pupal wing possess at first an arrangement 

 entirely different from that which they will assume in the imago. The abrupt termination of 

 the veins at H'.M'. is extremely distinct. 

 Fig. 19. Natural size. The outline of the left fore wing of the imago of Vanessa Atalanta, for com- 

 parison with the last figure. The position of the dark markings on the fringe is indicated by 

 thickenings. The bay is seen to be somewhat deeper than in the corresponding pupal line 

 (H'.M'. fig. 18). 

 Fig. 20. x 7. The left pupal wings of Vanessa Io. In the dark varieties of this pupa the pigment is 

 distributed along H'.M'. in a manner which suggests a former fringe. The dark parts along 

 the margin are diagrammatically indicated by thickenings, and it is seen that they correspond in 

 number and position with the dark parts of the fringe of the imago of V. Atalanta and C. cardui 

 (compare figs. 17 and 19). This is all the more remarkable because the imago of V. Io does 

 not possess a black-and-white fringe like the other allied forms. Inasmuch as the two former 

 are the more ancestral, as shown by their less indented hind margins, and especially by the 

 arrangement of their markings, it is probable that the condition of the dark pupae of V. Io 

 points towards the former existence of a black-and-white fringe in the imago of this species. 

 Fig. 21. Natural size. The outline of the left fore wing of the imago of Vanessa Io, for comparison 

 with the last figure. The imaginal hind margin is seen to be decidedly more sharply indented 

 than the corresponding part of the pupa (H'.M'. fig. 20). 

 Pig. 22. x 7. The left pupal fore wing of Vanessa polychlorus. The cuticular pigment is represented 

 as accurately as possible. The relation of the pigment and the traces of the venation to the 

 future imaginal hind margin (H'.M'.) are very distinctly shown. 

 Fig. 23. Natural size. The outline of the left fore wing of the imago of Vanessa polychlorus, for 

 comparison with the last figure. The hind margin is seen to be slightly more indented than 

 the corresponding line upon the pupa (H'.M'. fig. 22). 



