II 



FLIES WITH AQUATIC LARVAE 



137 



shape, which it is not here necessary to describe. It 

 will be enough to realise that the epidermis of the 

 future prothorax cannot be sacrificed to the folds 



FIG. 41. Process of formation of the parts of the head of the fly in the larva of 

 Chironomus (male). A, the new epidermis thrown into complicated folds, 

 which have been cut away in places to show the parts within. B, the same parts 

 in horizontal section. Ic, larval cuticle ; //", transverse fold ; (/"', upper wall of 

 do. ; ;, cut edge of new epidermis ; ant, larval antenna ; an, nerve to do. ; ant', 

 antenna of fly ; If, longitudinal fold ; o, eye of fly ; on, optic nerve ; an ', root of 

 antennary nerve ; br, brain ; as, oesophagus ; b, bulb of antenna of fly ; s, s, s', 

 blood-spaces. 



which are to give rise to the head of the fly. All 

 interference between the two developing structures is 

 obviated by the provision of a transverse fold, which 

 pushes into the prothorax from the neck, and forms a 



