x PHYLUM ARTHROPODA 249 



plants or even animals. The deposition of eggs by means 

 of ovipositors in the leaves or other parts of plants gives 

 rise to swellings galls in the interior of which the young 

 Insects are protected and nourished. In the case of many 

 Insects the eggs are enclosed in a cocoon ; in others they are 

 enclosed in gelatinous or waxy material. 



In some instances the young Insect, when it escapes from 

 the egg, has exactly the form of the parent, except that 

 sometimes the wings have not yet grown. But in most 

 instances there is a metamorphosis. This may be com- 

 paratively slight and gradual, the adult Insect differing 

 from the larva only in comparatively unimportant points, and 

 the segments and appendages of the latter becoming directly 

 converted into those of the former. Such a metamorphosis 

 is said to be incomplete. The term complete is applied to the 

 metamorphosis of the majority of Insects, in which the larva 

 differs so markedly from the imago, or perfect Insect, as 

 regards external form, the nature of the appendages, and 

 internal organisation, that there is need of a quiescent or pupa 

 stage during which the whole animal, or a considerable 

 part of it, undergoes an entire transformation. The 

 Lepidoptera (Fig. 133) may be taken as a good example 

 of such a complete metamorphosis. The larvae, or 

 caterpillars, are worm-like, but with well-developed jaws, 

 three pairs of jointed thoracic legs, and a number of 

 unjointed stumpy abdominal legs. Eventually the cater- 

 pillar spins a cocoon of a silky substance, enclosed within 

 which, and covered with a tough skin, it passes through a 

 quiescent or pupa condition the chrysalis stage. From 

 this the imago subsequently emerges with all the parts of 

 the adult Insect fully formed. 



In mode of life there is a very considerable difference 

 between different orders and families of Insects. Some are 



