Mosquitoes 



8 9 



of the labrum. Others think that its presence 

 causes a greater flow of blood to the wound. But 

 the sad part of it is, for us at least, that it hurts 

 and may cause malaria and possibly other dis- 

 eases. 



HOW MOSQUITOES BREATHE 



Mosquitoes and other insects do not have any 

 nostrils nor do they breathe through any open- 

 ings on the head. Along the sides of the thorax 

 and abdomen is a series of very minute open- 

 ings known as the spiracles. Through these the 

 air passes into a system of air-tubes, the tracheae. 

 There are two main trunks or divisions of the 

 tracheae just inside the body-wall and a number of 

 shorter connecting trunks. From these larger 

 vessels arise a great number of smaller ones which 

 branch and subdivide again and again until all 

 the tissues are supplied by these minute little air- 

 tubes that carry the oxygen to all parts of the body 

 and carry off the waste carbon dioxid. These air- 

 tubes are emptied and filled by the contractions 

 of the walls of the abdomen. When the body-wall 

 contracts the air is forced out of the thin-walled 

 trachea through the spiracles; when the pressure 

 is removed they are refilled by the fresh air rushing 

 in. 



