GNATS 



27 



thorax has a pair of feet tipped with hooked bristles which 

 secure a firm hold ; the next nine segments are devoid of out- 

 growths. The eleventh has two pairs of delicate tubes projecting 

 from it : these are filled with blood which circulates through them, 

 and are special respiratory organs. The twelfth segment also has 



FIG. 17. A, male ; B, female ; C, antenna of male ; D, antenna of female chironomus. 



four similar though small tubes, and also a pair of " feet " armed 

 with hook bristles for the sake of attachment to the walls of the 

 tube. On the dorsal surface of the twelfth segment are two 

 tufts of long bristles which are probably tactile in function. 



The " blood- worm " then differs from the " wriggler " in its 

 power to abstract oxygen from the water, and in having no 



