384 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 larvee occur among insects. (a) In many 
ametabolic and hemimetabolic forms the larva is somewhat 
like one of the lowly Thysanuran insects (Campodea), and is 
A 6 
Fic. 186.—Life history of the silk-moth (Bombyx mor). 
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 defined, three pairs of locomotor thoracic limbs, 
and mouth-parts adapted for suction. (4) The other type 
is worm-like or eruciform, ¢.g. the caterpillars of Lepidoptera 
(Fig. 186, 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 antennze, mouth-parts suited for 
biting, three pairs of jointed clawed thoracic limbs (corre- 
