MORPHOLOGY OF THE LEPIDOPTEROUS PUPA. 253 



The tAvo species of the genus Orgyla are small moths as compared with the majority 

 of Boml)yces: the larva of one species {0. cmtiqua) eats almost anything, while that of 

 the other {0. gonostigma) feeds on large trees ; and it is known that in the former case 

 the eggs do not all hatch at once, hut produce larvse in batches over a period of ten 

 weeks. Furthermore, the larvte are brightly coloured, and possess " tussocks " and 

 eversible glands as defensive structures ; and it is known that they are disagreeable to 

 certain insect-eating animals. Hence the species of this genus have escaped from the 

 conditions which render flight necessary for oviposition, and the eggs are laid all over 

 the cocoon. The female moth has an immense abdomen, and therefore can lay a very 

 large number of eggs, so as to ensure that many larvse shall reach some food-plant. The 

 degenerate wings and antenna} of the commoner species have been already described 

 and compared with the less degenerate organs of the pupa, and the autennaj with those 

 of the male. Another family of the Bomhychuc are even more degenerate — the 

 Psychidce : many of these escape from the above-mentioned conditions by their extremely 

 small size, and all of them are specially defended because their larvse live in cases, and 

 are therefore protected against many foes. Furthermore, the larva-case, in or upon 

 which the female moth always remains, is fixed to the food-plant, so that there is no 

 chance of the larvae wandering. The food-plants (when known) are amply large enough 

 for the small larvae to feed upon without fear of starvation. The wings of the female of 

 one of the less degenerate species {Fumea nitklella) have been described and compared 

 with those of the pupa (Plate XXVII. fig. 14). The examination of the pupa of one of 

 the more degenerate species (fig. 15) renders it equally clear that the female imago has 

 undergone degradation from a more perfect condition. 



Hence the causes of degeneration among the females of the Bonibycince appear to be 

 sufficiently clear. Equally degraded forms are also met with among the Tineina and 

 the Geometrina. Of the former no more need be said, for everything that has been said 

 of the Fsychid(B applies to them. 



Among the Geometers degenerate females wdth functionless wings are met with in 

 5 genera — Pliigalia (1 species), Nyssia (2 species), Jlyhernia (5 species), Anisopteyyx 

 (1 species), and Cheimatobla (2 species). The circumstances under which such females 

 appear in this large group of feeding moths support the explanation which is offered 

 above. The first two genera include Bombyciform moths, of which the males have 

 much-feathered antennae while those of the female are thread-like. I think it is very 

 probable that they do not feed, and the moths make their appearance at a time of the 

 year which does not encourage feeding by providing many different kinds of bloom, 

 although plenty of food exists for those moths which need it ; besides, the low tem- 

 perature itself tends towards inactivity when flight is unnecessary. P. pilosaria appears 

 in February and March : its larva feeds on oak. N. zonaria appears in September in 

 the North of England : its larva feeds on yarrow. N. hispidai'ia appears in February 

 and March, and the larva feeds on oak. The same explanation (season) holds with even 

 more force for the next three genera. In the genus Hyhernia, as the name implies, tht; 

 perfect insects emerge in the winter. II. rt<2)lcapraria appears in January and the first 

 half of February : the larva feeds on whitethorn, Iflackthorn, and oak. II. leucopheariu 



SECOND SEUIES. — ZOOLOGY, VOL. V. 38 



