146 NATURAL HISTORY OF AQUATIC INSECTS CH. 



the flics of Chironomus associate in swarms, which 

 arc bcHeved to consist entirely of males. The male 

 fly has large plumose antennze with their dilated 

 bases almost in contact. In the female fl}-, the 

 antennse are smaller and simpler, and their bases are 

 separated by an appreciable interval. The stomach 

 of the fly is usually empty or nearly so, and it is 

 probable that like many other winged Insects, it 

 never feeds. 



The laying of the eggs of Chironomus is attended 

 with some special difficulties. It is convenient that 

 the eggs should be laid in water, and that they should 

 float on the surface, where they can get a fair supply 

 of air, and run no risk of being smothered in silt or 

 organic refuse, but they must not float free, for the 

 water of a running stream would carry them to great 

 distances, and perhaps lodge them in some very un- 

 suitable place, or even sweep them out to sea. These 

 requirements are met in the case of Chironomus and 

 some other Insects by laying the eggs in chains, and 

 mooring them at the surface of the water. The eggs 

 are invested by a gelatinous envelope, which swells jj 

 out the moment it reaches the water into an abundant 

 transparent mucilage. This mucilage answers more 

 than one purpose. In the first place it makes the 

 eggs so slippery that Birds or Insects cannot grasp 

 them : it also spaces the eggs, and enables each to 

 get its fair share of air and sunlight. The gelatinous 

 substance appears to possess some antiseptic property 

 which prevents water-moulds from attacking the eggs. 

 Long after the eggs have hatched out, the transparent 

 envelope remains unchanged. During the summer 



