LIFE-HISTORIES OF INSECTS 



399 



respiratory apertures, and with tracheal gills or folds, while 

 the adults are winged and aerial, and breathe by open 

 tracheae. 



These insects are called hemimetaboUc , i.e. they have a 

 partial or incomplete metamorphosis. 



(3) Very different is the life-history of all other sets of 

 Insects— ant-lions, caddis-flies, flies, fleas, butterflies and 

 moths, beetles, ants, and bees. From the egg there is 

 hatched a larva (maggot, grub, or caterpillar), which lives a 

 life very different from the adult, and is altogether unlike 

 it in form. The larva feeds voraciously, grows, rests, and 



Fig. 221. — Life-history of the silk-moth (Bombyx mori). 



A., Caterpillar ; B, pupa ; C, imago ; the cocoon is cut open to 

 show the pupa lying within. In the caterpillar note the three 

 pairs of true legs in the anterior region, and the five pairs- 

 of pro-legs in the posterior region. 



moults. Having accumulated a rich store of reserve 

 material in its " fatty body," it finally becomes for some 

 time quiescent, as a pupa, nymph, or chrysalis, often within 

 the shelter of a cocoon. During this period there are great 

 transformations ; wings bud out, appendages of the adult 

 pattern are formed, reconstruction of other organs is 

 effected. Finally, out of the pupal husk emerges a minia- 

 ture winged insect of the adult or imago type. 



These insects are called holometabolic, i.e. they exhibit a 

 complete metamorphosis. 



Two kinds of larvae occur among insects, (a) In many 



