58 Elementary Zoology. 



not diffsrent in structure from the minute newly hatched larva. 

 It then becomes quiescent, and secretes a dense chitinous coat, 

 which covers its nearly motionless body. This is the pupa 

 stage, which is further protected by the cocoon, the well- 

 known silk produced by the larva from certain glands, which 

 entirely envelops it. From the pupa, after a certain lapse of 

 time, emerges the moth — the imago, or perfect insect, as it is 

 called. 



The caterpillar is a segmented creature with so great a like- 

 ness between the successive segments that a vermiform appear- 

 ance results. Hence the general term of " worm " popularly 

 applied to insect larvae, especially to those with no legs. The 

 head of the caterpillar has a pair of small antennse, sessile eyes 

 (differing in structure from the compound faceted eyes of the 

 adult), a pair of strong biting mandibles, and a plate behind the 

 mouth which corresponds to the next two pairs of appendages 

 fused together. After the head follow three segments, which 

 constitute the thorax ; each of these has a pair of jointed walk- 

 ing legs. Then comes an abdomen of ten segments (possibly 

 with a terminal eleventh). Not all of these segments have 

 limbs, but the third to the sixth, and the last, have fleshy 

 " prolegs " armed with terminal hooks. 



When the larva reaches a certain size it becomes a pupa. 

 The pupal stage is quiescent ; the pupa, when touched, will 

 exhibit movements, and in many moths which enter the pupal 

 stage in burrows in wood the pupa moves towards the surface 

 just before the time of emergence of the imago. But, broadly 

 speaking, the pupal stage is quiescent. During this period of 

 rest important changes take place. The tissues of many of the 

 organs break down, and are reconstructed into the definitive 

 organs of the imago ; to this remarkable histological process 

 the term " histolysis " has been applied. The pupa much more 

 resembles the perfect insect than it does the larva. The 

 appendages of the imago, its wings, and compound eyes, are 

 visible in the pupa, while the external reproductive orifices 

 are visible by marks. The number of segments in the pupa 

 appears to be the same as in the larva, i.e. certainly ten 

 abdominal segments and three thoracic. 



