ARTHROPODA 



19 



a weapon of defense provided with poison ii;lan(ls. P'roni its nature the 

 sting is essentialh' onlj' possessed Ijy the females. 



Some insects on leaving the egg develop directly to the adult stage, 

 the larva in most cases differing from the adult prin- 

 cipallj' in the absence of wings. In such cases there 

 is a slight change of form with successive molts, 

 the wings being ultimately acquired. Here the meta- 

 niorphic process is not thorough, and is therefore 

 referred to as incomplete metamorphosis. The ma- 

 jority of insects when hatched from the egg bear 

 no resemblance to the adult, and there is no observ- 

 able gradual approach to this form. The larva is 

 characteristically worm-like and an active and vora- ^-^e bee, s^howing 

 cious feeder, a number of molts occui'ring with the compound eyes, the 

 increase in size during this stage. There then ^^^'^'' °celli, and the 



. , iv 1 1 1 1 IX J. antennee. — Magm- 



mtervenes between the larval and adult stages a fied (after Orton, by 

 period of pupation, during which the animal is qui es- Dodge; Copyright, 



'cent and a series of changes ^^^tke'S ■ ""''" * 



occur m the body. At the 



conclusion of these changes the pupal case 



splits and the imago emerges, which, with 



the unfolding of the ap- 

 pendages and hardening 



of the cuticle, has in all 



essentials developed into 



the complete sexual 



adult. In this form 



of development the 



changes are distinct, and 



the process is referred 



to as complete meta- 

 morphosis (Fig. 8). 

 The duration of life 



in insects, including the 



■stages of the egg, larva, 



pupa, and adult, usually 



does not extend beyond 



a year. With quite a 



number it is much 



shorter than this, while 

 Fig. 9.-Diagram of terrai- with others it may be a 

 nal segments of arthropod leg, matter of Several years. 



£.... 



with mu,scies. a articulation; ^^ extreme example of 



f, flexors; e, extensors (after . ' . 



Boas, by Kirkaidy& Pollard), larval longevity bemg 



Fig. 8. — Metamor- 

 phosis of the House Fly, 

 showing oval, larval, 

 pupal, and adult stages. 

 On the right is an en- 

 largement of the foot; 

 on the left, the foot pad, 

 showing sticky, glandu- 

 lar hairs: on upper left, 

 a tsetse fly (from photo- 

 graph of drawing by 

 author). 



