370 INSECT TRANSFORBIATIONS. 



with their dances, and desirous of enjoying the full 

 effect of the sunbeam: if you approach, they are 

 instantaneously in motion again. Attempt to entrap 

 them with your net, and they are under the water and 

 dispersed in a moment. When the danger ceases, 

 they re-appear and resume their vagaries. Covered 

 with lucid arnwur, when the sun shines they look Hke 

 little dancing masses of silver and brilliant pearl.* 



The gyrations of the whirlwig are equalled in 

 vapidity by its diving, when its sports are intruded 

 upon by our approach. Its great quickness of sight, 

 indeed, is quite surprising; and is to be accounted for 

 by one of the most striking instances of providential 

 contrivance with which we are acquainted. Land 

 animals see indifferently under water, and aquatic 

 animals imperfectly in air; and an animal with an 

 eye equally fitted for seeing in water and in air, 

 can, on account of the great difference of the me- 

 diums, possess but imperfect vision in either. The 

 little whirlwig, to obviate this difficulty, is furnished 

 with two sets of eyes, one pair being placed on the 

 upper part of the forehead for seeing in air, and 

 another pair on the under part of the forehead, ex- 

 actly under the first, and separated from them by a 

 thin membrane, for seeing in water. As it swims 

 half submerged, the latter pair of eyes must be 

 very useful in warning the insect of approaching 

 danger, from fishes or rapacious larvae below, while 

 the former watch with equal keenness the ap- 

 proach of enemies above. The hind feet are no less 

 admirably formed for swimming, being broad, thin 

 and elastic; while the fore feet are constructed to 

 answer the purpose of hands for the seizing of prey. 

 The little animal is, besides all these wonderful 

 organs, furnished with a pair of ample wings for 

 transporting itself, should the water of its native 



* Intr. vol. ii, p. 372. 



