The Transformation of Chironomus 1 19 



the adult insect, are formed. The arguments long ago 

 employed by Swammerdam, or a careful study of what 

 happens in the transformation of any moth or butterfly. 

 Avould be enough to refute such notions. The parts in 

 question are complete (to outward appearance, at least) 

 when the pupal stage begins, and can often be revealed 

 by dissection before the pupal stage approaches. The 

 microscopic rudiments of the imaginal organs can some- 

 times be found in a very young larva, or even in the 

 embryo. 



In the Muscidae, which happened to be the first 

 Dipterous insects to be thoroughly investigated, the 

 unlikeness of the larva to the winged fly becomes 

 extreme. Buried in its food, the larva requires no limbs, 

 and only a vestige of a head. The fly, on the contrary, 

 is elaborate in structure beyond almost all other insects. 

 more elaborate by reason of the simplicity of the maggot. 

 It undertakes all the functions connected with the 

 choice of a site and food suitable for the larva, and the 

 contrast in activity and intelligence is as striking as 

 the contrast in form. 



Chironomus is less complex in its latest stage, more The trans- 



1 • • 1 1 , 1 Tin 1 formation 



complex m its larval stage, than a blow-fly, or perhaps of chiro- 

 any other Muscid. Hence its transformation, though 

 difficult to make out, is much more intelligible than that 

 of the Muscidae, upon which the labours of a generation 

 of entomologists have already been bestowed. Other 

 Dipterous insects are simpler than Chironomus in par- 

 ticular points, such as the development of the imaginal 

 head and its appendages, but taking it as a whole, 

 Chironomus is, of all the well-known Dipterous types, the 

 fittest for an elementary study of imaginal development. 

 What may be conveniently called imaginal folds often 

 play a great part in the development of the new organs 

 of an insect. In the simplest cases they are shallow 



