HEX A PODS. 



133 



Fig. 191. —Larva of Polyphemus moth (Telea polyphemus). 



opment as scale-like pads within the larval skin, no trace of them being visible from 

 the exterior. In the larvse of other insects which undergo a complete metamorphosis, 

 the abdominal append- 

 ages may be reduced in 

 number, and may be en- 

 tirely wanting, and even 

 the thoracic legs may 

 disappear. 



When about to pass 

 into the pupal stage, the 

 silk-worm spins a fine 

 thread, which it coils into 

 an oval case known as the 

 cocoon. Frequently in 

 spinning this cocoon 

 leaves are included, so 

 that the envelope is a compound of silk and leaves. Other forms do not spin a cocoon, 

 but, with this exception, the process of metamorphosis is essentially the same. Now 



by a moult the pupal condition is attained. The 

 body is enveloped in a chitinous integument, 

 and on the anterior and ventral portions may 

 be seen the sheaths which cover the wings, 

 legs, antennae, and mouth-parts. In the form 

 under discussion these sheaths are all closely 

 united to the body, but in others (e. g. beetles) 

 these parts are all distinct and separate. The 

 length of pupal life varies from a few days or 

 weeks to several months, and in the case of some beetles evidence is not lacking to 

 support the opinion that the pupal stage may last for many years. 



At last the insect is ready to enter its perfect state. It moults for the last time 

 and emerges from its pupal envelopes. In the case of the Lepidoptera, the wings are 

 moist flabby sacs, but soon they are distended by fluids which are forced into them, 

 and then, drying rapidly, they acquire the firmness necessary for their use as organs of 

 flight. By taking a moth when it has just emerged from the cocoon, one can easily 

 produce deformed wings by pinching or puncturing these members, thus preventing 

 their distension. 



In the moth which we have taken as the type of complete metamorphosis, the 

 mouth-parts have lost their capacity for biting, and some 

 of them have been converted into a long tube adapted 

 for sucking the nectar of flowers, the antennae are trans- 

 formed from short and inconspicuous organs into long 

 feathery feelers, the compound eyes appear, the thoracic 

 legs become longer and more slender, and the full com- 

 plement of joints is produced, while the pro-legs of the 

 abdomen have entirely disappeared. 



Correlated with these external changes so superficially reviewed are as great and 

 important modifications of the internal organs. The reproductive organs acquire 

 their adult functions, the digestive organs become adapted to the changed food, the 



Fig. 192. — Cocoon of Telm. 



Fig. 193. — Pupa of TeUa. 



