20* LIFE HISTORY AND HABITS. 



lives a similar life. At each moult it grows larger and gradually changes, 

 almost imperceptibly, till it is full grown. There is no caterpillar, no 

 chrysalis ; there are no sudden changes at any moults ; the wings grow 

 slowly; the reproductive system is developed gradually; there is no 

 period of rest, and the insect feeds at every stage of its life. We may 

 concisely state that whilst the grasshopper develops gradually, the 

 butterfly does so suddenly. The sudden change from caterpillar to chry- 

 salis, and chrysalis to butterfly, is one distinguishing feature ; this is 

 called the metamorphosis, and all insects which pass through these 

 changes are said to have a " metamorphosis/' It is a convenient word 

 which expresses the facts that (1) the young insect is totally unlike the 

 mature insect ; (2) between the two is the resting stage similar to that we 

 call chrysalis. We might divide all insects into two groups, those which 

 are caterpillars and chrysalides before they become butterflies, and those 

 which change gradually and slowly till they become grasshoppers. 

 The first have a metamorphosis, the second have none. Speaking gen- 

 erally, all insects belong to one group or the other. They either have 



FIG. 29. 

 The perfect Insect. 



metamorphosis and pass through four stages, viz., (1) the egg ; (2) a 

 stage like the caterpillar (called larva) ; (3) a stage like the chrysalis 

 (called pupa) ; (4) the mature stage like the butterfly (called imago] ; or 

 they have no such distinct stages but commence as eggs, pass through 

 a series of gradual changes during which we may call the insect a nymph, 

 to the perfect insect, called the imago^ 



It will be seen that we have here a character that sharply divides all 

 insects into two groups. There are some insects which have a partial 



1 Larva, plural larva ; pupa, plural pupce ; imago, plural imagines ; nymph, plural 



