METAMORPHOSIS OF INSECTS. 



3'5 



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

 ametabolic and hemimetabolic forms the larva is somewhat 

 like one of the lowly Thysanuran insects (Campodea), and is 

 therefore called campodeiform. It has the regions of the 

 body well defined, 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. 138, A), with three pairs of limbs; the more modified 

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

 and the degenerate maggots of flies (Fig. 139, A), etc., not 

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



Fig. 138. — Life history of the silk-moth (Bombyx mori). 



A, caterpillar ; E, 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. 



pillar has often several pairs of abdominal pro-legs, which 

 may be homologous with legs, and other abdominal append- 

 ages are known on the larvae of other insects, and even in 

 the embryos of some whose larvae are campodeiform. These 

 facts make it likely that the primitive form had many legs. 



The larvEe of Insects vary enormously in habit and in structure, and 

 exhibit numerous adaptations to conditions of life very different from 

 those of the parent. Thus caterpillars, which are usually plump and 

 tense, so that a peck from a bird's bill may cause them to bleed to death, 

 even if no immediate destruction befall them, are protectively adapted 

 in many different ways. Their colours are often changed in harmony 

 with those of theii surroundings ; some palatable forms are saved by 



