Insects and their world 



Fig. 49. A hover-fly, Order Diptera 



projecting spines which grip surrounding surfaces. When the insect is 

 clear of obstructions the skin spHts and the adult emerges. It is present 

 practice to reserve the term 'pupa' for the quiescent stage during which 

 the larva is being remodelled into an adult, and to say that the active 

 movements we have just described are really made by the adult still in 

 its pupal skin. It is then called a 'pharate adult'. 



Walkings Running and Jumping 

 Four-legged animals have two quite different ways of moving their legs, 

 A horse when walking or trotting moves the near fore-, off hind-, near 

 hind- and off fore-legs, in the familiar chp-clopping rhythm. This is 

 clearly based on a twisting movement of the body, the fore-quarters 

 twisting to the right while the hind-quarters twist to the left. On the 

 other hand, when a horse gallops it changes to an up-and-down bending 

 of the spine, with the two hind-legs moving together. 



Insects likewise have two tjpts of motion rather similar to these, 

 except that the movement is largely confined to the legs, and does not 

 twist the body so much. The first movement is rather more complicated 

 when there are three pairs of legs to manage. In principle, the fore and 

 hind near legs go forward, together with the off middle, while the insea 

 remains balanced on a tripod formed from the other three legs; then 



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