122 THE BOOK OF NATURE STUDY 



legs are flattened structures fitted alike for swimming and for 

 propelling the light body on the surface film. The fore-limbs 

 are considerably longer, and are used for grasping. The antennae 

 have a characteristic double appearance, and the eyes are 

 worth special note. They appear to be double, being divided 

 into two parts to enable the beetle to see both above and below 

 the water. Whirligigs are not very easy to keep in the aquarium, 

 first because they are very apt to spread their wings and escape ; 

 and second, because it is difficult to supply them with sufficient 

 food. Their activity at the surface seems to be 

 determined by the fact that they largely depend 

 upon small insects, such as flies and beetles, 

 which fall into the water, and these naturally are 

 not common in the aquarium. If well-fed, and 

 prevented by means of a piece of gauze from 

 making their escape they will, however, thrive, and 

 FIG. 56. A whirii- t ne active movements make them engaging occu- 

 beetle (Gyr- pants of the tank. The eggs are laid on water- 

 natator}. plants, and the larvae, which hatch in about a 

 week, are very curious. They are whitish in colour, have strong 

 jaws, the usual three pairs of legs, and in addition in the ab- 

 dominal region a paired series of respiratory processes, which 

 stretch out at the sides of the body, and because of their leg-like 

 appearance give the little larva the appearance of a centipede. 

 Pupation is carried on outside the water on the stem of a 

 water-plant, where a little greyish cocoon is formed. The 

 whirligigs, of which we have a number of species, are much 

 smaller than the beetles previously mentioned ; the commonest 

 species is not more than about \ inch in length. 



The whirligigs and Dyticus and Hydrophilus all belong to the 

 Coleoptera, or Beetles. Very different are the water-boatman 

 and its allies, which, though as beautifully adapted for aquatic 

 life as the water-beetles, are yet really related to the bugs. These 

 insects have a suctorial instead of a biting mouth like a beetle, 

 have the anterior wings partly hard and partly membranous, and 

 have an active pupa stage, or in other words, an incomplete 

 metamorphosis. 



The water-boatman (Notonecta glauca) is very common in 



