56 METAMORPHOSIS 



the adaptations are so slight that the term naiad is scarcely 

 applicable. 



Larvye may be defined as immature insects which leave the 

 egg in a relatively early stage of morphological development. 

 In general, they differ fundamentally in form, structure and 

 behaviour from the imagines. Their mouth-parts and other 

 appendages usually exhibit marked or even profound differences 

 of form and structure, while lateral (or adaptive) ocelli, with only 

 very rare exceptions, are the functional visual organs. Throughout 

 larval life the reproductive system is in a very rudimentary 

 condition. Coenogenetic development has become so highly 

 specialised that transformation into the imago has involved the 

 intercalation of a quiescent pupal instar in the ontogeny. Prior 

 to the assumption of the pupal condition, the developing buds 

 of the genitalia, wings and other appendages lie concealed beneath 

 the body-wall. 



In the present discussion the term Hemimetabola has been used to 

 include both the Hemimetabola stnsu stricto and the Paurometabola of 

 many authorities. The differences exhibited by the transformations in 

 the two cases are essentially those of degree. 



In Giard's interpretation, the Hemimetabola {sens, kit.) undergo 

 transformation as opposed to true metamorphosis which is featured 

 only in the Holometabola. 



Types of Larvae 



Insect larvae may be grouped into three principal types depend- 

 ing upon the stage in their ontogeny in which eclosion from the 

 egg takes place. In addition to these a fourth type, derived from 

 the third, has to be recognised. 



1. The Protopod Type. This type is characteristic of the 

 primary larva? of certain species of endoparasitic Hymenoptera. 

 The eggs in such species are either almost devoid of yolk, or but 

 poorly supplied with nutrient material, and the young larvae 

 consequently issue at a very early ontogenetic stage of develop- 

 ment. Their survival is rendered possible from the fact that they 

 are enclosed either in the eggs or bodies of their hosts, where 

 they develop immersed in an abundance of easily assimilated 

 food, usually in the form of yolk or of ha^molymph. 



