688 TEXT-BOOK 01' ENTOMOLOGY 



tive canal. We have seen, as Korsehelt and Heider state, that the 

 formation of the mesodermal organs of the imago (muscles, con- 

 nective tissue, fat-body) begins in the mesodermal part of the 

 imaginal buds, whose first origin is still obscure. Simultaneously 

 with the formation of the imaginal organs, there goes on under the 

 influence of the leucocytes the destruction of the larval organs. 

 Both processes (destruction and regeneration) therefore go on hand 

 in hand, so that the continuity of the organs in question in most 

 cases remains perfect, inasmuch as the complete destruction only 

 ensues after the formation of the final organs. The only exceptions 

 are most of the muscles of the larva, which are destroyed at a very 

 early period. 



Moreover, it is evident that the sharp division into larval, pupal, 

 and imaginal stages only applies to the external surface of the 

 body, since they follow one another after successive moults. The 

 processes of the internal development, on the other hand, form an 

 entirely continuous series of transformations between which is no 

 sharp line of demarcation. Yet as a whole the form of the larva, 

 pupa, and imago are kept distinct in adaptation to their separate 

 environments and habits. 



Finally, as Pratt very truly remarks, the epigenetic period in 

 insects, when new organs are forming, does not end with the birth 

 of the larva from the egg, but extends through the larval, and even 

 through the pupal period. " The principal significance of the pupal 

 period and the metamorphosis is that it is the time when the larval 

 characters which were adapted for use during a period of free life in 

 the midst of the development, and which would be valueless to the 

 imago, are corrected or abandoned." 



HYPERMETAMOEPHISM 



When an insect passes through more than the three normal stages 

 of metamorphosis, i.e. the larval, pupal, and imaginal, it is said to 

 undergo a hypermetamorphoais. The best-known examples are the 

 supernumerary .stages of Meloe, Stylops, etc. 



