256 ANIMAL LIFE 



from eggs arranged in spiral lines on a flat gelatinous 

 sheet. The larva is of a glassy transparency, and lies 

 still and horizontal below the surface of the water, 

 only changing its position by an instantaneous jerk, 

 and again floating motionless. The momentary 

 gleam as it turns reveal its presence, and has gained 

 for it the name phantom-larva. Upon closer ex- 

 amination these organisms are found to resemble 

 fig. 52. The head bears antennae, two complex eyes, 

 and a peculiarly constructed mouth enclosed between 

 the two lips and the jaws. At the back of the throat 

 is a fringe of stout bristles arranged like the bristles 

 of a lobster-pot, so as to strain the food, the result 

 being that no opaque substances collect in the body 

 and break the transparency of the larvae. The food 

 itself consists, according to some authorities, of small 

 creatures which are caught by the antennae and 

 chewed up in the mouth ; according to others, Core- 

 ^ra-larvae feed on the fine microscopic life of ponds. 

 The horizontal attitude of the larva in the water is 

 aided by two pairs of vesicles filled with air or gas. 

 These air-sacs are special expansions of the reduced 

 tracheal system which runs as a closed pair of tubes 

 down the body, and is filled by diffusion. 



The further history of Corethra resembles that of 

 the gnat. The organs of the fly appear as convolved 

 protuberances. A pair of air-trumpets sprout from 

 the thorax and lead into a new system of tracheal 

 vessels. The old tubes break down, and the contained 

 gas collects into a bubble beneath the thorax. The 



