354 CHARACTERS OF INVERTEBRATE ANIMALS 



a disagreeable odour, due to the secretion of certain glands which 

 open on the under-side of the third segment of the thorax. Some 

 are terrestrial and others aquatic. Many of the land bugs are 

 not among the personal enemies of man, but feed on the juices 

 of plants. These forms mosriy escape the observation of those 

 who are not entomologists, but the wingless blood-sucking bed- 

 bug {Cimex lectularius) has an effective way of compelling 

 attention that has rendered it the most widely known among its 

 order. Even more odious are the small wingless forms known 

 as lice which infest the bodies of human beings and many other 

 animals, multiplying with astonishing rapidity. They are regarded 

 as bugs which have become degenerate as a result of their parasitic 

 habit. A typical example is the Head- Louse {Pediculus capitis), 

 which feeds on the blood of the scalp, and lays its eggs on the 

 hairs, to which they are firmly attached. 



The water-bugs comprise a number of forms familiar to the 

 student of fresh-water life, and to some extent known even 

 to the casual observer. The skaters, which are often seen 

 gliding about on the surface of the water, are of this kind, or, to 

 speak more accurately, constitute a family allied both to land- 

 and water-bugs. The Needle-Bug {Limnobates stagnorum), with 

 long attenuated body and deliberate movements, is conspicuous 

 among them. The Pond-Skater {Gerris paludurn) has a stouter 

 body and moves very rapidly. One genus {Halobates) is especially 

 interesting in being a marine form living upon the surface of the 

 sea even at great distances from land. This is remarkable, for 

 though insects are exceedingly dominant as terrestrial forms, and 

 are far from uncommon in fresh water, they are almost unrepre- 

 sented in the marine fauna. 



Water-bugs proper are inconspicuous insects distinguishable 

 from their terrestrial allies by their extremely-reduced antennae, 

 and by the fact that they actually live in the water and not merely 

 on it like the skaters. The Water-Scorpions are rapacious narrow- 

 headed forms, in which the fore-legs are used for seizing their 

 prey. The narrow tail-like prolongation which has suggested 

 the common name is an arrangement connected with breathing, 

 as will elsewhere be described. In some species there is a broad 

 flat body {e.g. Nepa cinerea), while in others it is long and narrow 

 {Ranatra linearis). Equally common are the broad bodied 

 Water- Boatmen [Notonecta), which, by means of their long hair- 



