366 



EVOLUTION AND ANIMAL LIFE 



the protecting wax scale, and dies. From the eggs hatch active 

 Uttle larval scale bugs with eyes and feelers and six legs. They 

 crawl from under the wax scale and roam about over the orange 

 tree. Finally, they settle down, thrust their sucking beak 

 into the plant tissues, and cast their skin. The females lose 

 at this molt their legs and eyes and feelers. Each becomes a 



mere motionless sac capable 

 only of sucking up sap and 

 of laying eggs. The young 

 males, however, lose their 

 sucking beak and can no 

 longer take food, but they 

 gain a pair of wings and an 

 additional pair of eyes. They 

 fly about and fertilize the 

 saclike females, which then 

 molt again and secrete the 

 thin wax scale over them. 



Throughout the animal 

 kingdom loss of the need 

 of movement is followed 

 by the loss of the power 

 to move, and of all struc- 

 tures related to it. 



Loss of certain organs 

 may occur through other 

 causes than parasitism and 

 a fixed hfe. Man}^ insects 

 live but a short time in 

 their adult stage. May flies 

 live for but a few hours - 

 or, at most, a few da3^s. They do not need to take food to 

 sustain life for so short a time, and so their mouth parts have 

 become rudimentary and functionless or are entirely lost. 

 This is true of some moths and numerous other specially short- 

 lived insects. Among the social insects the workers of the 

 termites and of the true ants are wingless, although they are 

 born of winged parents, and are descendants of winged ancestors. 

 The modification of structure dependent upon the division of 

 labor among the individuals of the community has taken the 

 form, in the case of the workers, of a degeneration in the loss of 



Pig. 226. — The black scale, LecaniuTti olece', 

 and its parasite, the tiny chalcid fly, Scu- 

 tellista cyanea; and the ladybird beetle, 

 Rhizobius ventralis. (After Isaacs.) 



