hi \ i i OMfl 



Significance of Metamorphosis. "The eMentia] feattu 



morphosi- Shaipj "appeal In be the -eparalion ill li: 



and development and the limitation of the reprodm t ive prote 

 short period at tin- end of the individual life." 



The simplest insects. Thy^amira, have no metamorpho>i-. and ] 



of ever having had one. Hence it is inferred that t h< 

 Is had none; in other words, the phenomenon of metamorpho-i- 

 originated Liter than Insects themselves. SuCO in the 



evolution of metamorphosis are illustrated in the various ord 



inse< 



The distinctive mark of the simplest metamorphosis, as in Orthop 

 ml Hemiptera, is the acquisition of wings; growth and sexual 

 development proceeding essentially as in the non-metamorphic in 

 ( Thy san ura and Collembola). Here the development of wings does not 

 interfere with the activity of the insect; its food habits remain unaltered; 

 throughout life the environment of the individual is practically the same. 

 Kven when considerable difference exists between the nymphal and 

 imaginal environments, as in Ephemerida and Odonata, the activity of 

 the individual may still be continuous, even if somewhat lessened as the 

 period of transformation approaches. 



With Xeuroptera, the pupal stage appears. In these and all other 

 holometabolous insects the larva accumulates a surplus of nutriment 

 sufficient for the further development, which becomes condensed into 

 a single pupal stage, during which external activity ceases temporarily. 



With the increasing contrast between the organization of the larva 

 and that of the imago, the pupal stage gradually becomes a necessity. 

 Metamorphosis now means more than the mere acquisition of wings, for 

 the larva and the imago have become adapted to widely different en- 

 vironments, chiefly as regards food. The caterpillar has biting mouth 

 parts for eating leaves, while the adult has sucking organs for obtaining 

 liquid nourishment; the maggot, surrounded by food that may be ob- 

 tained almost without exertion, has but minimum sensory and locomotor 

 power- and for mouth parts only a pair of simple jaws; as contrasted 

 with the fly, which has wings, highly developed mouth parts and sense 

 organs, and many other adaptations for an environment which is 

 strikingly unlike that of the larva; so also in the case of the higher 

 llymenoptera. where maternal or family care is responsible for the help- 

 condition of the larva. 



Thus it is evident that the change from larval to imaginal adapta- 

 tions is no longer congruous with continuous external activity; a quies- 



