SOME AQUATIC INSECTS 87 



being kept under observation, they should be 

 placed in a tank with quite a shallow water 

 supply, or they will inevitably drown, for they 

 experience very considerable difficulty in rising 

 from any depth to the surface of the water to 

 take in a fresh supply of air. 



Should we when hunting on a summer after- 

 noon for aquatic insects, chance upon a stagnant 

 pool or ditch, the bottom of which is well 

 covered with fallen leaves, but whose surface 

 is free from duckweed, we shall have an oppor- 

 tunity of observing every stage in the life-history 

 of the Common Gnat (Culex) ; a life-history that 

 is of the greatest interest and significance, 

 because it is practically identical with that of 

 the dread Anopheline Mosquito which is ithe 

 transmitting agent of malaria from man to man. 



Over the surface of the pool innumerable 

 Gnats are performing endless airy dances. If 

 we catch a few, and examine them closely, we 

 shall see that they differ slightly from one 

 another, the most marked feature being the 

 difference in the appearance of the antennae, 

 which in some of the captured specimens stand 

 out from the head like beautiful plumes, while in 

 others they appear almost like little wires 

 sparsely clothed with short hairs. Should we 

 carry our examination a little further, and 

 observe with the aid of a magnifying glass the 

 mouth-parts of the two kinds of Gnats which we 

 have collected, we shall find still more remark- 

 able modifications of structure, for we shall see 

 that all those specimens which have simple 

 antennae have their mouth-parts highly developed 



