212 INTRODUCTION TO ZOOLOGY CHAP, xiv 



out the larval life, with a sudden greater change becoming 

 apparent at the last moult, as for example in dragon-flies. 

 Such a development is known as " incomplete metamorphosis," 

 and the developing larva, as soon as signs of wings are visible 

 externally, is known as the nymph. 



The changes that take place internally during the pupal 

 stage vary. The phenomenon is strangest in such forms as the 

 Blow- fly. Here the full-grown maggot detaches its outer 

 skin which hardens into a kind of capsule or cocoon, and inside 

 this, the whole body disintegrates into a creamy mass within 

 a delicate membrane, and from this shapeless mass in a few 

 days there gradually evolves the intricate body of the perfect 

 blow -fly. 



The Insecta are divided into eight orders, distinguished 

 from each other by the number and texture of the wings, by 

 the modification of the mouth-parts, by the nature of the 

 metamorphosis, and by the form and habits of the larva and 

 pupa. 



These eight orders are : 



1. Lepidoptera Butterflies and Moths. 



2. Coleoptera Beetles and Ladybirds. 



3. Orthoptera Cockroaches, Grasshoppers, and Earwigs. 



4. Rhyncota or Water-bugs, Plant-lice, Scale Insects, etc. 



Hemiptera. 



5. Neuroptera May-flies, Dragon-flies, Caddis-flies, Stone-flies, 



Alder-flies, Lacewing-flies, etc. 



6. Diptera All two-winged flies, Gnats, etc. 



7. Hymenoptera Ants, Bees, Wasps, Gall -wasps, Saw-flies, 



Ichneumon-flies, etc. 



8. Aptera Spring-tails and Silver-fish. 



