354 



PHYLUM ARTHROPODA. 



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 

 miniature 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 

 ametabolic and hemimetabolic forms the larva is somewhat 

 like one of the lowly Thysanuran insects ( Campodea\ and is 



FIG. 186. Life history of the silk-moth (Botnbyx mort). 



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 four pairs 

 of pro-legs in the posterior region. 



therefore called campodeiform. It has the regions of the 

 body well denned, three pairs of locomotor thoracic limbs, 

 and mouth-parts adapted for suction, (b} The other type 

 is worm-like or cruciform, e.g. the caterpillars of Lepidoptera 

 (Fig. 1 86, A), with distinct head and limbs; the more modified 

 grubs of bees, etc., with distinct head, but without limbs ; 

 and the degenerate maggots of flies (Fig. 187, A), etc., not 

 only limbless, but with an ill-defined head. A typical cater- 

 pillar has a cylindrical body often "hairy," a distinct hard 

 head, simple eyes, small antennae, mouth-parts suited for 

 biting, three pairs of jointed clawed thoracic limbs (corre- 



