Identification and Classification of Insects 411 



2. Incomplete Metamorphosis. — In this type the egg develops into a 

 nymph, specifically known as a naiad (ni' ad) (Gr. naias, water nymph), 

 which does not resemble the adult in general characteristics or in man- 

 ner of life. In each of the orders that possess incomplete metamorphosis 

 the naiads develop in water, with aquatic respiratory organs, while the 

 adults are terrestrial (aerial) with air-breathing organs. The changes 

 in body form are more marked than in gradual metamorphosis but are 

 much less marked than in complete metamorphosis. Briefly, the stages 

 are egg, aquatic naiad, terrestrial, aerial adult, egg (Fig. 205). 



Thorax 

 I Eye 



Antenna 



Hypopharynx 



^lahiufn 



„ ^pipharynx 

 .--.Mandible 

 — Maxilla 



Fig. 202. — Piercing-sucking mouth parts of a mosquito (Culex sp.) of the order 

 Diptera. Mouth parts are separated and enlarged. 



Fig. 203. 



Fig. 204. 



Fig. 203. — Snow flea (Achorutes nivicola) of the order Collembola, much en- 

 larged. (From Kellogg: American Insects, Henry Holt & Co.) 



Fig. 204. — Springtail (Achoreutes armatum) of the order Collembola, much 

 enlarged. A spring beneath the tip of the abdomen for springing purposes is not 

 shown. (From Popenoe: Mushroom Pests and How to Control Them, U. S. 

 Department of Agriculture, courtesy of Bureau of Entomology and Plant Quaran- 

 tine.) 



