THE EXTERNAL MORPHOLOGY OF THE LEPIDOPTEROUS PUPA. 47 



the same facts are well seen among " the degraded females " of certain 

 Geometrids, for the wingless female oiNyssia zonaria possesses thread- 

 like antennas very different from those of the male, although the pupal 

 antennas do not greatly differ in size. The similarly degenerate female 

 of Hybernia defoliaria emerges from a pupa with comparatively broad 

 antennas. Poulton concludes that the evidence offered by the antennas 

 shows that when an imaginal organ falls into disuse and shrinks, the 

 corresponding pupal organ shrinks at a very much slower rate, and so 

 " presents a picture of the long-past condition of the former." 



The pupal wings are lateral appendages to the mesothorax and 

 metathorax and are generally folded round the venter of the first 4 

 abdominal segments, the apices of the fore-wings frequently meeting 

 on the median line of the venter of the 3rd or 4th abdominal 

 segment. Usually, but little of the hind-wing can be clearly made 

 out, and then only the hind marginal border, which generally extends 

 just beyond the base of the inner margin of the fore-wing. The fore- 

 wing gives distinct traces of neuration (often differing considerably 

 from that of the imago, at other times agreeing therewith). Poulton 

 makes the general statement that "over the part of the pupal fore-wing 

 beneath which the imaginal wing will develop, lines which correspond 

 to the future neuration are more or less plainly visible. The 

 pupal neuration ceases at Poulton's line, although the direction 

 of the neuration lines may be continued by irregular lines of pigment 

 across the interval between the pupal and future imaginal hind 

 margins. These irregular continuations are, however, very different 

 in character from the more defined appearance of the lines which 

 represent the neuration, and, when the latter are studied in especially 

 favourable species, e.g., Pt/rameis atalanta, they are seen to correspond 

 exactly with the future neuration of the imaginal wing. This is all 

 the more remarkable inasmuch as the main tracheae within the pupal 

 wing, which will ultimately be enclosed as important elements in the 

 imaginal nervures, possess at this time an arrangement different from 

 that which they will then assume." 



With regard to the pupal neuration, Midler (Kosnws, i., p. 390) was 

 the first to observe that its ontogenetic features could be utilised for 

 phylogenetic purposes. He observed that, in the immature pupa of 

 Castnia ardalus, the transverse nervures were wanting and that different 

 longitudinal ones, which afterwards more or less completely dis- 

 appeared, were present, and hence he regarded the pupal neuration as 

 the primitive one. This view Spuler adopted, and, by stripping off the 

 loose skin of a larva just beginning to pupate, examined the incipient 

 neuration of the wings of the young pupa. He then placed the living 

 pupa in Avater when, the process of thickening and resulting conceal- 

 ment of the nervures of the wing being retarded, the tracheal branches 

 became slightly enlarged, filled with air, and could thus be more easily 

 seen. (Small pupae from which the larval skin has just been cast and 

 which are transparent are the fittest objects for examination.) He 

 shows further that the transverse nervures are of secondary and sub- 

 ordinate importance, and Packard {Bombycine Moths of America, p. 85), 

 by means of two figures of Gracilaria syringella, one of the neuration 

 of the imaginal fore-wing, the other of that of the semipupal fore- 

 wing, shows that the generalised neuration of the latter is similar to 

 that of Eriocrania. 



