BRITISH LEPIDOPTERA 



CHAPTER I. 



METAMORPHOSIS IN LEPIDOPTERA. 



It is impossible to deal with the pupal stage of Lepicloptera (at 

 any rate so far as relates to the internal condition of the pupa) without 

 first obtaining some idea of the nature of metamorphosis, the essential 

 features of which, in insects, appear to be the separation of the periods 

 of growth and development, and the limitation of the reproductive 

 processes to a comparatively short time at the end of the individual 

 existence. 



Although it is not our intention to enter into a consideration of 

 the general question of metamorphosis in insects, one or two points 

 may claim our attention. We may look upon the embryonic life of an 

 insect as its life within the ovum, or we may consider it as including 

 the whole of that period of existence extending from the beginning of 

 yelk segmentation to the acquisition of the mature form. In some 

 insects most of these changes take place in the egg stage, in others a 

 great many modifications take place afterwards, i.e., in the larval and 

 pupal stages. Our ordinary idea of embryonic life, being based largely 

 on the conditions existing in placental mammalia, is slightly different 

 from either of these. The embryonic stage may, in this sense, be 

 defined as lasting until a stage is reached which is like that attained 

 at maturity, except in size and capacity for reproduction. 



The primitive Thysanurid insect is a hexapod and ceases embryonic 

 life when it quits the egg, having, by this time, except in size and 

 maturity, acquired its adult form ; it moults as it increases in size, but 

 does not change its appearance. The Orthopteran, which is also more 

 or less a primitive form, has almost acquired its adult appearance on 

 leaving the egg ; it moults a certain number of times, and at the last 

 moult acquires wings. By this further piece of evolution the previous 

 stages may be termed embryonic. In this respect the young Orthop- 

 teran is as much an embryo as the lepidopterous larva. 



The lepidopterous larva has been evolved from, and represents the 

 active (quasi-adult) larva of Orthoptera, and is, in a sense, its direct 

 descendant. Its vermiform aspect has been acquired by change from 

 the active hexapod state (still represented by the Orthopteran nymph), 



