316 INSECTS. 



are long in the land species ; in the aquatic they are 

 shorter, of three or four joints, and are hidden from 

 sight in furrows beneath the head. 



Ocelli are sometimes present, and are two in number. 



As in Homoptera the fore-part of the thorax is some- 

 times of unusually large proportions, so in Heteroptera 

 is the scutellum, or little shield, a triangular plate ex- 

 tending over part of the abdomen (PI. XIII., fig. 6, &c.), 

 and which, in the Plant Bugs is sometimes so large as 

 nearly to cover the wings. 



The tarsi have never more than three joints ; most 

 of the land species give out a disagreeable scent. 



The Iarva3 and pupse are active, and resemble the 

 perfect insect. 



Heteroptera is divided into two sections. 



1. HYDROCORISA, which contains the aquatic species. 



2. AUROCORISA, containing the terrestrial. 

 Hydrocorisa contains two families, Notonectida3 and 



Nepidee. 



To the first belong the well-known Water Boatmen. 

 Their shape is somewhat boat-like, and the resemblance is 

 increased by the two long hind-legs, which, extended on 

 either side, as the animal lies back downwards in the 

 water, exactly represent a pair of oars, both in appearance 

 and action. 



The Notonecta Glauca (PL XIII., fig. 1) is a common 

 insect, and certain to attract attention from its size, from 

 its singular position as it floats with the under-side upper- 

 most,* head depressed, tail (for the purpose of respira- 

 tion) just touching the surface, and extended oars, and 

 from the swiftness with which one stroke of these fringed 



* Whence its name. 



