mSFX:!TS OR HEXAPODA. 



143 



interest. That insects have the sense of smell well developed 

 we know for certain. Whether the palpi or the antennae, or 

 both, are connected with this sense is not quite clear ; most 

 probably the antennae are chiefly functional in this respect. 

 The sense of vision is acute, as any one knows who has tried 

 to catch an insect settled on some flower ; whilst we cannot 

 doubt that taste is as surely present, when we consider the 

 partiality certain insects have for certain foods. 



To return once more to the changes through which an insect 

 goes — the so-called metamorj)hosis. Insects which pass through 



S 



Pig. 67.— Alimentary Canal of Larva {Tlpula paludosa). 



a, Mouth ; h, gullet ; c, proventriculus ; e, Cfeca ; d, stomach ; /, hepatic tuhes ; 

 g, small intestine ; i and h, large intestine ; j, rectum ; k, anus ; I, anal gland. 



the stages enumerated on p. 141, in which the larva is quite 

 unlike the adult, and where there is a distinct quiescent pupa, 

 in which the larva is transformed into the imago, are said to 

 undergo a complete metamorpliosis. There are many insects 

 which have no quiescent pupal state, and where the larva is 

 very similar to the adult. The whole life-cycle from the egg 

 onwards is one of activity except when the insect is moulting. 

 The pupal stage is simply distinguished by the small swollen 

 wing-buds seen at the sides of the thorax. These insects are 

 said to have an inconvplete or gradual metamorphosis. 



Insects are classified partly by the structure of the mouth, 

 partly by the structure of the wings, and also by their meta- 



