366 MANUAL OF VEGETABLE-GARDEN INSECTS 



others the transformation is abrupt and striking. In the 

 former case the insect is said to have an incomplete meta- 

 morphosis ; in the latter a complete metamorphosis. 



Incomplete metamorphosis. 



In this type of development, the immature stages resemble 

 the adult in form. The wings develop externally as pad-like 

 outgrowths of the thorax but do not become functional till 

 the adult stage is reached. The immature forms are known 

 as nymphs. In this type of development, the life cycle of the 

 insect consists of three stages, viz., the egg, the nymph (three to 

 five instars) and the adult. The true bugs and grasshoppers 

 have incomplete metamorphosis. 



Some authors refer to the early nymphal stages of plant-lice 

 as larvpe and to the last nymphal stage, in which the wing-pads 

 are present, as pupje. According to this system in the thrips, 

 the first two nymphal stages are called larv?e, the third stage 

 a prepupa and the fourth a pupa. These terms are somewhat 

 confusing and are not followed in the present work. It is 

 preferable to restrict the terms larva and pupa to the early 

 stages of insects having a complete metamorphosis. The 

 various stages of an insect with incomplete metamorphosis 

 are shown in Fig. 232. 



Complete metamorphosis. 



In this case the immature stages of the insect bear little or 

 no resemblance to the adult. The wings develop internally 

 in pockets formed by an infolding of the body-wall of the thorax. 

 The immature stages are known as larvre. The larva molts 

 five or six times, and when full-grown transforms to an inactive 

 pupa, often in a cocoon or earthen cell prepared by the larva. 

 The pupa is a resting stage in which the organs of the larva 

 are more or less broken down and made over into those of the 

 adult. In the pupa, the antennae, legs and wings of the adult 



