114 INJURIOUS AND USEFUL INSECTS 



the hinder end of its body out of the tube, and the thin-walled 

 gills, which are all placed near the hinder end, are thus brought 

 into action. 



The pupas of Chironomus can be fished up from the same 

 streams as those in which the larvae dwell, or they may be 

 reared in captivity by placing full-grown larvae in a suitable 

 vessel, and waiting for the time of transformation. The pupa 

 usually lies half in and half out of the mud, and 

 sways the fore part of its body to and fro for 

 respiratory purposes. After two or three days 

 it becomes buoyant, and floats at the surface. 

 The pupa consists of the body of the future 

 fly, enclosed within a transparent pupal skin. 

 It is provided with certain peculiar temporary 

 organs — viz. a broad, fringed tail-fin, and two 

 bunches of branching filaments, given off just 

 behind the head. These filaments are the pupal 

 respiratory organs. They wave to and fro in 

 the water, and by some process, which cannot 

 be satisfactorily explained in the present state 

 of our knowledge, extract air, or rather oxygen, 

 from the water. The head, legs, wings, and all 

 other parts of the future fly are shrouded within 

 the close-fitting pupa-skin. Not only are they 

 externally complete, but they are fully developed 

 in almost every microscopic detail. The pupal 

 stage of Chironomus is not so much a time of 

 growth, as a brief period of adaptation to a new 

 and very different set of external conditions. 

 Fi^. 63. -Pupa The many complex organs of the fly, such as 

 siS'^xT"'"" the elaborate and beautiful antennae, the com- 

 pound eyes, each of many facets, the slender 

 and many-jointed legs, and the gauzy wings, cannot be ex- 

 temporised. A long time is necessary for their development. 

 The whole pupal stage is brief, lasting only two or three 

 days, and even before it sets in, the parts of the fly are 

 already formed. It is clear, therefore, that the development 

 of the new organs must have been long in progress at 

 the time of pupation. On careful examination of a full- 

 grown larva this conclusion is confirmed. The thoracic 

 segments shortly before pupation become visibly enlarged, and 



