4 INTKODTTCTION. 



abdomen, or supported in an upright attitude by a cremaster or 

 silken cable passed round it and attached to contiguous objects, as 

 in various groups oiPapillones; or, in many iVocto'rfcc, Ceratocamjndce^ 

 etc., simply buried in the earth. 



The Pfpa. 



Having formed its cocoon, the larva turns to a pupa, during 

 which stage in some Diptera almost the whole of the tissues of the 

 body undergo degeneration into a liquid fatty substance within the 

 outer cuticle, except the nerve centres and some bodies attached to 

 them known as the "imaginal disks,"' which are the rudiments 

 of the future body, wiugs, and legs, and which by absorption of the 

 products of the degenerated tissues gradually grow and build up 

 the imago till ready to emerge from the pupa skin. In the Lepi- 

 doptera, however, this process is not carried nearly so far ; the- 

 dorsal vessel and its muscles, some skin muscles, the tracheal system, 

 and the alimentary canal of the larvae are persistent, and the mouth- 

 parts, antennae, and legs of the imago are modified and developed 

 from those of the larvae : the process, in fact, resolving itself into 

 the imaginal structures not present in the larvae being developed 

 from disks, whilst the larval structures not present in the imago 

 undergo degeueration. 



The various parts of the pupal skin are all soldered together 

 and immovable, except certain of the abdominal somites, but the 

 head with the cases for the proboscis and antennae, the thorax with 

 the wing- and leg-cases, and the abdominal somites can be easily 

 distinguished. 



Emekgence fkom Cocoon." 



In the orders of insects of which the imagines are provided with 

 jaws, these are used to help them to force their way through the 

 cocoon, and Eriocepliala being provided with functional jaws pro- 

 bably uses them for the same purpose. The evolution of the 

 haustellate Lepidoptera resolves itself into the solution in various 

 ways of the problem of freeing themselves from the cocoon without 

 jaws *. In this respect the families fall into two main divisions t : — 

 (1) The Incompletce, with the 7th abdominal segment free in the 

 male, fixed in the female, the moth emerging from the cocoon 

 clothed in the effete pupal skin ; of these Micropjteinjx % uses the 

 jaws of the pupal skin to rupture the cocoon and to pass through 

 it and overlying earth, motion being induced in them by vermicular 

 movements of the pupa. In all other Lepidoptera the pupal jaws 

 are functionally obsolete, accompanied by considerable consolidation 

 of the previously movable parts, and a roughening of the dorsum 



* Dr. T. A. D. ChapmaD, Trans. Ent. See. 1896, pp. 567-587. 

 t Id., Trans. Ent. Soc. 1893, pp. 97-119. 

 + Id., Trans. Ent. Soc. 1893, pp. 255-265. 



