508 The Outline of Science 



joints being arranged as shears for cutting through plant roots 

 (see figure facing page 312). The "Praying Mantis" and the 

 Water- Scorpion both show the fore-legs modified into pincer- 

 like traps for seizing prey. Usually the middle pair is not greatly 

 modified, but in some water-bugs, like the Water-boatman, the 

 middle legs are the longest and have become effective oars for row- 

 ing on the surface of the water. The hind pair of legs of many 

 insects is elongated for jumping, as in grasshoppers and locusts 

 and some beetles. Certain beetles and bees and wasps have a 

 "comb" or bristle-lined cavity on the leg by means of which they 

 clean their feelers, while some butterflies use their feeble front legs 

 to brush off dust from their heads. Ants are particular about their 

 toilet. In the course of the day's work an ant's antennae may be- 

 come soiled. On its first pair of legs it is provided with what we 

 may call brushes and combs, as we have described, and the ant 

 may be seen to draw its besmeared antennae through this brush- 

 and-comb arrangement on the fore-legs. One of the legs will 

 be passed over its head and body, its other legs sweeping off 

 every particle of "dirt." No cat is more fastidious over its toilet. 

 Ants will even wash and brush each other, just as they will 

 exchange greetings, as they meet, by movements of their antenna;. 

 The hind-legs of bees show a modification for pollen-gathering, 

 a broadening of the "shin" to make a "basket," into which the 

 pollen is swept by special bristles. 



Insect's Breathing 



Breathing takes place by means of a system of air-tubes or 

 tracheae which penetrate to every hole and corner of the body. 

 Trachea? arise as inpushings of the skin, and the layer of chitin 

 which lines them is continuous with that which covers the whole 

 body. In the larger air-tubes this chitin is thickened spirally in 

 threads, and this keeps the tubes from collapsing. Air enters 

 the body by openings (spiracles or stigmata) occurring on most 

 of the body-rings. 



