480 THE INSECT WORLD. 



The Gyrinid&y which come very near to the Dytiscida, like 

 water which is clear and a little agitated. They are small 

 black insects, living in troops, and which swim with rapidity, 

 describing incessantly capricious circles, which has gained for them 

 the name of " Whirligigs. " They are remarkable for the disposi- 

 tion of their eyes, which are double ; so that the GyrinidfB 

 seem to have four eyes. The lower ones look into the water and 

 watch for the prey or the fish that advances as an enemy ; whilst 

 the upper eyes look upwards towards the air, and warn the insect 

 of the approach of enemies from above. To escape from fish, the 

 Gyrinus jumps out of the water, and also makes use of its wings ; 

 to escape from birds, it dives rapidly. This activity, and this 

 double sight, make the capture of the Gyrini a task of great 

 difficulty. They must be surprised with a net. At the moment 

 of being seized, they emit a milky and fetid liquid. 



The females lay their eggs end to end, on the leaves of aquatic 

 plants. The larvae are long and narrow, and of a dirty white. 



Fig. 494. - Gyrinus natator. Fig. 495. Larva of Gyrinus natator. 



They come out of the water at the end of the summer, and form 

 for themselves a cocoon on the plants bordering the banks. After 

 a month, the perfect insect is hatched, and plunges into the water. 

 The Gyrinus striatus (Fig. 496) is found in the waters of Southern 

 Europe. 



All these species are of small size, and do not exceed a fifth of 

 an inch in length ; but in the tropics we find Gyrini two-thirds of 

 an inch long. One of these species, distinctus, exists in the little 

 lake of Solazies, in Reunion Island, noted for its mineral waters. 

 The patients amuse themselves by fishing for this insect, with a 



