286 



METAZOAN PHYLA 



Some insects exhibit in their Hfe history even more than the four 

 stages — egg, larva, pupa, and adult. In some beetles there are two types 

 of larvae, one with legs and caterpillar-like, the other without them and 

 maggot-like, and one of these types follows the other. This condition 

 is known as hypermetamorphosis. In other cases a subimago stage 

 precedes the adult, or imago stage, the change from subimago to imago 

 involving a molt and a modification of certain details of structure. 



Fig. 191. — Life history of a holometabolous insect, a butterfly, Danaus archippus 

 Fabricius. a, egg. b, larva, c, pupa, d, adult. Natural size, (a to c from Jordan and 

 Kellogg, " Animal Life," by the courtesy of D. Appleton and Company; d, from a specimen.) 



316. Autotomy.— Some insects possess the power of autotomy, but 

 regeneration is known to occur regularly only in the walking sticks. 

 An example of autotomy is presented by the locust; if held by the hind 

 leg and pressure is made on the femur, it will break off this leg. Termites 

 and ants have deciduous wings, which are shed after swarming. 



317. Injuries Due to Insects.— Insects affect man injuriously in 

 a great many ways. They may annoy him by their presence or by 

 their bites or stings. The insect may be poisonous and its attack may 

 cause effects which are painful though rarely of themselves serious. 

 Insects may also be the means of transmitting disease-producing organ- 



