]8 INTRODUCTION. 



it swims on its back, i.e. with its legs above its body ; whereas the 

 CorixcB swim back up with the legs below the body. 



The smaller Boatmen, of which there are about twenty species, 

 are known as Corixa (plate 7, fig. 71), and their wings fold flat along 

 their backs. They are similar in habitat to the former, largely 

 vegetarian in their diet however. The mouth parts show an entirely 

 different construction from those of Notonecta glauca, which are in 

 the form of a hollow pointed beak adapted to piercing their. prey 

 and sucking the juice therefrom. It is curious to see a swarm of 

 them sporting on a sunny afternoon. At first glance it looks as 

 though a good rise of Blue Duns was going on, but closer observation 

 will show that after a short flight they drop into the water again, 

 and swim away amongst the water weed. Woe betide them should 

 the trout observe their little game, which then has a tragic ending ! 

 The Water Measurers (plate 7, figs. 73-74) also belong to this class 

 (Hydrometra stagnorum ; Gerris lacustris). They are known to 

 anglers as " Water Crickets," and are to be found at the margin 

 of almost all waters. In the early season they are taken very readily 

 by the fish before more luscious morsels are abundant. They are 

 insectivorous, and at once attack and crowd round any small insect 

 which alights on the water near them. 



There are also illustrated two other Hemiptera, the Frog Hopper 

 or Cuckoo Spit (Aphrophora alni), plate 8, fig. 91, which is the 

 " Wren Tail," of Ronalds ; in the summer it hides in a frothy mass 

 on the stems of grass and plants, and in the autumn, where these 

 are near the water, this insect sometimes jumps on to the surface 

 by thousands. Another of the Hemiptera is the common Grass Bug 

 (plate 8, fig. 88) ; it is singularly like the Water Measurers in general 

 form, but is found on the grass in the pastures, and along the margins 

 in countless numbers, and on a windy day is often blown on to the 

 water in thousands. There is also a green one, similar in form, but 

 slightly smaller than the one illustrated. 



We will close these brief notes with a short one on the Spiders 

 (Araneida), which occupy an intermediate position in the animal 

 kingdom between the insects and the vertebrates. The external 



