INSECTS AT LARGE 



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parent-forms, they are said to be heterometabolous ( ) ; 



such insects hatch as nymphs ( ), a wingless form 



gradually growing larger and larger wings after each ecdysis until the 

 adult form is reached; holometabolous ( ), if there 



is a complete metamorphosis, such as being born a worm-like larva 

 ( ), which takes food for a short time and then goes 



TniSc 



HtTraSc 



Fig. 215. 



A. Respiratory system of worker honey-bee as seen from above, one anterior 

 pair of abdominal sacs removed and transverse ventral commissures of abdomen 

 not shown. / sp, III sp, VII sp, spiracles ; HtTraSc, Tra Sc, 1, 2, 4, 7, 8, 10, 

 tracheal sacs ; Tra, tracheae. (From Snodgrass, Tech. Series 18, Bur. Ent., U. S. 

 Dep't of Agric.) 



B. A portion of the tracheal tissue of a cockroach, highly magnified. Only 

 parts of the tubes are in focus. 



cu., Cuticular lining with spiral thickening ; nu., nuclei of the protoplasmic 

 layer; ppm., protoplasmic layer continuous with the epidermis ( "hypodermis" ) of 

 the surface of the body. (After Borradaile). 



into a resting or pupal stage during which no food is taken, and during 

 which time it loses all its larval structures, finally developing into a com- 

 plete adult insect, known then as an imago ( ). 



In those cases where there is no metamorphosis, the animals are 

 said to be ametabolous ( ). 



