128 



Development zvithin the Larva 



the cavity of the invagination, and its concavity as well 

 as its deeply sunk position contrast strongly with the 

 convexity and exposed posijtion of the imaginal eye. The 

 imaginal antenna originates as a secondary duplication of 

 the invagination around the antennal nerve of the larva, 

 which duplication in all stages of growth is continued 

 up to the larval antenna. 



Fig. 99. — Formation of imaginal head in larva (male). A. The now epidermis 

 thrown into folds, which have been cut away in places. B. The same parts in 

 horizontal section. i!c, larval cuticle, t./, transverse fold. t.f\ iipper wall of 

 ditto, ep, epidermis. «i, cut edge of now epidermis, ant, larval antinna. 

 a.rj, nerve to ditto. ant\ antenna of ily. l.f, longitudinal fold. 0, eye of fly. 

 on, optic nerve, o.w', root of antennary nerve. 6r, brain, oss, oesophagus. 

 6, enlarged second joint (bulb) of antenna of fly. s, s, s', blood-spaces. (From 

 Miall's Natural History of Aquatic Insects, after Miall and Hammond, 1892) 



In larvae which are not far from pupation, the folds 

 are no longer confined to the region of the head. They 

 extend backwards into the prothorax. and the part which 

 forms the compound eyes comes to lie wholly behind the 

 larval head. This backward extension is not brought 



