334 



THE REASON WHY, 



' For he maketh small the drops of water : they pour down rain according to 

 the vapour thereof." JOB xxxv. 



1314. Why do we see, in tanks of rain water, insects 

 rising to the surface ? 



Because numerous insects pass through their first stages of 

 existence in water, and among them the common gnat. The gnats 

 of the previous season having deposited their eggs on the sides of 

 the water-butt, the warm water developes them, and the larvae of 

 the gnats appear (Fig. 81 ; c natural size of larva ; b larva 

 magnified). 



Fig. 81. LAEVA AND PTTPA OP GNAT. 



(Greatly magnified.) 



1315. Why do they continually rise to the surface of the 

 water ? 



Because they require to breathe air, and therefore they come up 

 to the surface, where, elevating the tube (b) above the surface of the 

 water, they are enabled to breathe. 



1316. Why do some appear to have larger heads than 

 others ? 



Those that have apparently larger heads, and that breathe 

 through tubes attached to their heads (d) are in the pupa, or 

 second stage of development, and underneath the large shield by 



