192 INSECT TRANSFORMATION 



own blood, a respiratory pigment which has the power of 

 seizing oxygen and holding it in a loose combination so that 

 it may be given up to the tissues of the body, as they need it 

 for the support of the combustion-processes that are always 

 going on in living matter. The head of the worm is also 

 frequently seen to emerge from the sheltering tube, the feelers 

 being directed to various points, and the jaws working strongly 

 to seize and break up the particles of decaying plant-substances 

 which serve these larvae for food. 



With the assumption of the pupal stage it is interesting to 

 observe a change in the position of the breathing organs. 

 Like the larva, the pupa (Fig. 100 c) lives under water, and a 

 flattened expansion of the tail-segment gives to it a certain 

 power of movement. At the front end of the thorax, just 

 behind the head, are situated a pair of outgrowths, commonly 

 in the form of delicate-branching, tufted filaments, but some- 

 times simply tubular, or clubbed. These, like the tail-pro- 

 cesses of the larva, are gills by means of which the insect in 

 this stage of its life-history obtains its supply of oxygen ; but, 

 unlike the larval organs, they contain prolongations of the 

 air-tube system, and are therefore tracheal gills. There is a 

 beautiful provision, by the degeneration of the very narrow 

 air-tubes at the bases of these organs, for their rupture at the 

 close of the pupal period, so that they are shed with the pupal 

 cuticle and not remade for the aerial imago which will not need 

 them. 



In the larvae of some members of the Chironomid group, it 

 is interesting to observe that special breathing organs, like 

 those just described, are absent, and the exchange of gases 

 goes on through the thin body-wall generally. Such is the 

 condition in the larva of the interesting little marine midges 

 (Clunio) with their feebly-winged males and wingless females. 

 The Clunio grub, essentially like that of a Chironomus without 

 special gills, feeds on green seaweeds and, visible only during 

 the low spring-tides, must be submerged in salt water for the 

 greater part of its life. 



Midges of the Chironomus group pass their larval existence 

 in ponds, ditches or sluggish streams. The allied sandflies 

 (Simuliidae) , whose females, though of small size, are often 

 voracious and even dangerous blood-suckers, have larvae 



