OF THE ORDER COLEOPTERA. '285 



But still they are marked by some particular characters 

 which constitute them a very distinct genus. 



The gyrini may, in general, be considered as small insects, 

 the species which is most known not exceeding the dimensions 

 of the common fly. Some species, however, are known 

 which are of a larger size. No insects exhibit, like them, 

 what may be termed four net-work eyes. It is very easy to 

 perceive them in looking at the animal from above, and then 

 examining it underneath: for the two lower eyes are con- 

 cealed underneath the head. The insect can see at the same 

 time, and by different eyes, the objects which are above its 

 head, and those which are below it. Accordingly its sight 

 is very good and piercing, the proof of which may be very 

 easily seen by placing it in a glass of water. After having 

 made at first a few turns in swimming, it remains at last 

 tranquilly on the surface of the water. The instant the 

 hand is approached towards it, or any movement is made, 

 without even touching the glass, it is seen of a sudden to 

 pvit itself into a state of agitation, and usually sink into 

 the water. 



These insects can make use of their wings, and do, some- 

 times, elevate themselves into the air, but the particular 

 conformation of the feet sufficiently indicate that they are 

 also destined to live in the water. 



The swiftness with which the gyrini swim on the surface 

 of the water, or in the water itself, is surprising. The eye 

 cannot follow the rapidity of their circumvolutions, and 

 various motions in all directions. As the coverings of these 

 insects are very smooth and shining, when the sun casts its 

 rays upon them, they seem like so many brilliant pearls in 

 motion, which reflect the light in different shades, and pre- 

 sent a very beautiful spectacle. 



They are almost always assembled in troops upon the 

 surface of the water, where they sometimes repose in a state 



