2 The Form of Insects 



these main divisions a Branch or Clan {Phylum) knit 

 together by the tie of a common ancestry. 



There is a Branch which comprises animals formed 

 of a number of segments placed one behind the other, 

 covered at least in part with a hard outer skeleton, 

 and feeding and moving by means of a number of pairs 

 of jointed limbs, some of which are used as feelers, 

 some as jaws, and others as legs. As members of 

 this Branch we at once recognise bees, beetles and 

 moths ; centipedes and millipedes ; scorpions, spiders 

 and mites ; crabs, lobsters and woodlice. By the older 

 naturalists all these creatures were called Insects, the 

 name being suggested by the division of the body 

 into sections. But nowadays it is usual to apply the 

 term Arthropods (jointed-legs) to the whole Branch, 

 and to restrict the term Insects to one of the classes 

 into which the Branch has been sub-divided. By 

 Insects, then, modern naturalists understand those 

 Arthropods the segments of whose bodies are, in the adult 

 state, grouped in three divisions : (l) a ivell-marked head 

 bearing one pair of feelers and (normally) three pairs of 

 jaws ; (2)0 fore-body (thorax) bearing three pairs of legs 

 and (usually) two pairs of wings ; and (3) a hind-body 

 (abdomen) without legs. Accepting this definition we 

 consider a Bee, a Dragonfly or a Cockroach to be an 

 insect ; but not a Centipede, which, though possessed 

 of a distinct head with feelers, has at least fifteen 

 pairs of legs -, nor an eight-legged Spider whose' head, 

 bearing no feelers, is not distinct from the fore-body ; 

 nor a Lobster, which also has the head fused with the 

 fore-body, and possesses two pairs of feelers, six pairs 

 of jaws and five pairs of legs, as well as a pair of 

 limbs on each segment of the hind-body. 



Having thus defined what is meant by an insect, 

 we pass on to examine in some detail the form and 

 structure of a typical member of the class. It is 



