21 



Among generalized forms where the appendages are soldered to- 

 gether, the cuticle of the exposed parts of the body contains hut very 

 little chitin, and is but slightly differentiated in texture from the cuticle 

 of the hidden surfaces. When the imago emerges, or even before 

 that time if the body is slightly pressed, the appendages separate very 

 readily from each other, and are not torn upon the emergence of the 

 insect, so that the pupal skin often remains complete except for the slit 

 on the dorso-meson through which the imago emerged. A very differ- 

 ent condition exists, however, among highly specialized forms. Here 

 the exposed portions of cuticle become very hard and firm, while those 

 which are not exposed are very thin and delicate and are almost en- 

 tirely destroyed at the emergence of the imago. The outer covering, 

 of course,, being so firmly soldered together, remains in one piece and 

 is apparently complete except for the slit through which the insect 

 emerged. This has led many to think that this outer chitinized por- 

 tion was the entire pupal skin and that it was a structure, analogous 

 perhaps to an egg shell, in which the pupa had been enclosed. 



Another remarkable difference between the generalized and the 

 highly specialized Lepidoptera lies in the fact that in the latter the ap- 

 pendages are not fully formed when pupation takes place, but con- 

 sist of the transparent cuticular coverings through which one or more 

 slender tracheae may be seen. The duration of the pupal stage doubt- 

 less influences this, there being a stronger tendency among highly 

 specialized forms to hibernate as pupae. 



During the life of the pupa the adult parts are developing, and be- 

 fore it is time for the imago to emerge, the cuticular parts of the adult 

 are fully formed. In the generalized families previously mentioned 

 and in some specialized forms where the pupal cuticle remains more 

 or less transparent, one is able to see a part of the development taking 

 place, especially in the case of the appendages. The scales appear on 

 the legs and wings and the color pattern may often be easily traced on 

 the latter several days before the emergence of the insect. This stage 

 of the insect, after the cuticular parts are fully formed, and while it 

 still retains its pupal skin, has been designated as the preimago*. If 

 the pupal skin is not already dark in color, it grows considerably 

 darker in the last few days before the insect emerges, and one is thus 

 able to determine when the preimago stage is reached. 



*Packard applied the term subimago to the corresponding stage in certain 

 Hymenoptera. This is an unfortunate use of the term as subimago had already been 

 applied to the first winged stage of the Ephemeridae. 



