Lymph and Larva 



201 



active larval life. The larval tissues and organs disin- 

 tegrate, and return to a sort of embryonic condition, 

 to be rebuilt in new form in the adult insect. 



With incomplete metamorphosis development is 

 more direct, there is no pupal stage, and the form of the 

 body is less altered during transformation. Metamor- 

 phosis is incomplete in the stoneflies, the mayflies, the 



dragonflies and dam- 

 selflies and in the 

 water bugs. The im- 

 mature stage we shall 

 speak of as a nymph. 

 All nymphs agree in 

 having the wings de- 

 v eloped externally 

 upon the sides of the 

 thorax. Metamor- 

 phosis is complete in 

 all the other orders 

 above mentioned. 

 Their immature 

 stage we shall call 

 a larva. All larvas agree in having the wings devel- 

 oped internally: they are invisible from the outside 

 until the pupal stage is assumed. It should be 

 noted in passing that "complete" and ''incomplete" 

 as applied to metamorphosis are purely relative terms. 

 There is in the insect series a progressive divergence 

 in form between immature and adult stages, and the 

 pupal stage comes in to bridge the widening gap 

 between. 



There is less change of form in the water bugs than 

 in any other group of aquatic insects. The nymph of 

 the water boatman (fig. 109) differs chiefly from the 

 adult in the undeveloped condition of its wings and 

 reproductive organs. 



Fig. 109. Water boatmen (Corixa), two 

 adults and a nymph of the same species. 



