ILLINOIS BIOLOGICAL MONOGRAPHS [ill 



SUMMARY 



The principal results yielded by this investigation of the postembry- 

 ology of noctuid larvae may be summarized as follows: 



(1) The number of molts is characteristic of species, altho influenced 

 to some extent by external factors. 



(2) The largest number of molts, the greatest amount of larval growth, 

 and the highest fecundity are three mechanically correlated conditions. 



(3) These three conditions represent a specialization, the larger number 

 of molts and higher fecundity having been derived from the smaller number, 

 which is correlated with lower fecundity. 



(4) The conditions of larval growth, number of molts, and higher 

 fecundity have arisen independently in different species. 



(5) An investigation of the postembryonic development of all external 

 structures of noctuid larvae has revealed the existence of many previously 

 undescribed changes. 



(6) Three factors have been identified as operating in the production of 

 the changes observed, recapitulation, adaptation to unequal function in 

 different stadia, and the mechanics of growth. 



(7) These factors may express themselves singly or in various combina- 

 tions, in which case they may operate either in the same direction or in 

 opposition to one another. 



(8) Recapitulation is essentially different from the other two factors in 

 that it is the expression of a general law, which fails to manifest itself oniy 

 when its effects are obscured by those of other factors. 



(9) When recapitulation and adaptation to unequal function con- 

 flict, the latter is dominant. 



(10) When the factor of unequal function becomes secondarily elimi- 

 nated, the recapitulative force remains unexpressed. 



(11) The postembryonic changes found have been classified according 

 to the factor or combination of factors responsible for them. This classifi- 

 cation is as follows: 



(I) Recapitulative. — Changes in the relative length of the epicranial 

 stem, in the extension mesad of the postgenae, and in the depth of the 

 labral cleft; the migration ventrad of the occipital setae, of the head setae 

 vl, v2,and probably fl; changes in the coloration of the head and body, in 

 the sculpturing of the cuticle, in the location of the body-setae, except those 

 of the first two pairs of larvapods, and in the form of the mandibles; the 

 reduction of the primary chitinization and acquisition of secondary chitin- 



