A BRITISH LEPIDOPTERA. 



and must not be considered as a persistence, after hatching, of the 

 vermiform embryonic stage that all insects pass in the egg. 



Thus, Thysanura is hexapod and active all through its life after 

 hatching from the egg, moulting and increasing in size, but without 

 any change of form. The Orthoptera are hexapod and active all 

 through life, after hatching from the egg, moulting and increasing in 

 size, and becoming winged at the final ecdysis. The true nature of 

 this view of metamorphosis is well illustrated by 2Mo'e and its allies, 

 which are hexapod and active when hatched, become vermiform and 

 more or less apod at the later moults, reassuming legs and becoming 

 winged at the last ecdysis. The Lepidoptera hatch with ill-developed 

 true legs and with special appendages (prolegs) for progression, 

 increase in size, and moult during the larval stage, having the true 

 legs developed in the pupal stage, and becoming winged and fully 

 hexapod in the imaginal stage. It may be assumed, therefore, that 

 the lepidopterous pupa represents the most ancestral form of the 

 Lepidoptera, and that the scale-winged imago and the vermiform larva 

 are both special forms evolved owing to the exigencies of environment 

 from an ancestral active form with many of the characters now only to 

 be observed in the pupal stage, and this notwithstanding the quiescent 

 condition of the lepidopterous pupa. "When, therefore, a larva is 

 referred to as being embryonic, it must not in any way be considered 

 that the stages through which it passes are a reversion to previous 

 vermiform stages that are passed in the ovum, nor as a more or less 

 direct continuation of these, but simply as being a series of specialised 

 changes that have become necessary to the success of the order and 

 that lead up finally to the assumption of the adult form. 



We have already seen (vol. i., ch. iii., pp. 16-23) that the lepi- 

 dopterous embryo in the egg rapidly passes through a number of 

 remarkable changes of form, and have hinted in the succeeding 

 chapters, that the larva, after hatching, undergoes equally great 

 and important modifications at each ecdysis in adaptation to the 

 different modes of life adopted by the various species ; but besides 

 these external changes in the form, structure, and general appearance 

 of the insect, there are other equally important changes occurring 

 simultaneously, viz., a change of the internal organs, and a change in 

 the physiological processes. It has already been hinted by Meldola, 

 and others, that the last factor is, possibly, the most important, and 

 that the change in external form is often only the outward manifesta- 

 tion of changed or modified physiological processes, and although, in 

 general, enquiries as to development have been largely directed to the 

 larval, pupal, and imaginal stages, it is well knoAvn (ride, vol. i., p. 51) 

 that insects leave the egg in differing stages of development (even 

 within the limits of the same family) , and many distinctions observed 

 in subsequent stages of metamorphosis may be the result of differences 

 in embryonic development. Not that we consider, as we have already 

 pointed out, that the larval instars are to be considered as continuous 

 of the changes occurring in the egg, but rather that some of the larval 

 changes may have been crowded back as it were into the egg stage. 

 With this limitation understood, we may premise by stating that the 

 term "metamorphosis" is applied to the changes that take place 

 between the hatching of the larva from the egg, and the period at 

 which the adult imaginal stage is finally reached. These changes are 



