24 



THE STUDY OF INSECTS 



the locust, when they emerge from the egg resemble in form the adult, 

 but still undergo some change, are said to undergo an incomplete meta- 

 morphosis. In other words, after leaving the egg they do not undergo a 

 complete change of form. 



There are many other insects besides locusts which have an incom- 

 plete metamorphosis. For example, crickets, cockroaches, aphids, the 

 true bugs, cicadas, scale- insects, et al. 



The young of three orders of insects, the stoneflics (Plecoptera) , the 

 mavrlies (Ephemerida) and the dragonflies (Odonata) are adapted for 



Fig. 42. — Nymph of Melanoplus, 

 first stage. (After Emerton.) 



Fig. 45. — Nymph of Melanoplus, 

 fourth stage. (After Emerton.) 



Fig. 4.?. — Nymph of Melanoplus, 

 second stage. (After Emerton.) 



Fig. 46. — Nymph of Melanoplus, fifth 

 stage. (After Emerton.) 



Fig. 44. — Nymph of Melanoplus, 

 stage. (After Emerton.) 



third 



Fig. 47. — Melanoplus, adult. 



living in the water and most of them pass through somewhat more com- 

 plicated changes than do the nymphs of locusts. For these reasons 

 perhaps they ought to be included in a group by themselves and desig- 

 nated as having a special phase of metamorphosis; but for the sake of 

 simplicity we have placed them among the insects having a gradual or 

 incomplete metamorphosis. 



The nymph. — The young of all insects with incomplete metamorphoses 

 are known as nymphs. The term nymph is applied to all stages of such 

 insects from the time they hatch until they shed their skin for the last 

 time. When a nymph first hatches it has no signs of wings; but after it 

 molts once or twice one or two projections appear on each side of the 

 thorax in the case of those forms in which the adult has wings. These pro- 

 jections become larger and larger and more wing-like in form with each 

 successive molt. 



The important feature of insects having an incomplete metamorphosis 



