Mosquitoes 



79 



well as for attacking and holding other larger 

 things. 



A few kinds feed habitually some distance be- 

 low the surface, others on the bottom, while still 

 others feed always at the surface. With one or two 

 exceptions, the larvae must all come to the surface to 

 breathe (Figs. 53-57). Most species have on the 

 eighth abdominal segment a rather long breathing- 

 tube the tip of which is thrust just above the surface 

 of the water when they come up for air. In this 

 tube are two large vessels or tracheae which open 

 just below the tip of the tube and extend forward 

 through the whole length of the body, giving off 

 branches here and there that divide into still smaller 

 branches until every part of the body is reached 

 by some of the small divisions of this tracheal sys- 

 tem that carries the oxygen to all the tissues. The 

 length of the breathing-tube is correlated with the 

 feeding-habits of the larvae. Anopheles larvae 

 which feed at the surface have very short tubes 

 (Fig. 58), others that feed just below the surface 

 have breathing-tubes as long or very much longer 

 than the ninth abdominal segment. The last seg- 

 ment has at its tip four thin flat plates, the tra- 

 cheal gills. These too are larger or smaller ac- 

 cording to the habits of the larvae. Those species 

 that feed close to the surface and have the tip of 



