PARASITISM AND DEGENERATION 197 
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 sac-like 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 structures related to it. 
103. Degeneration through other causes,—Loss of certain 
organs may occur through other causes than parasitism and 
a fixed life. Many insects live but a short time in their 
adult stage. May-flies live for but a few hours or, at most, 
a few days. 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 ‘com- 
munity has taken the form, in the case of the workers, of a 
degeneration in the loss of the wings. Insects that live 
in caves are mostly blind; they have lost the eyes, whose 
function could not be exercised in the darkness of the cave. 
Certain island-inhabiting insects have lost their wings, 
flight being attended with too much danger. The strong 
sea-breezes may at any time carry a flying insect off the 
small island to sea. Only those which do not fly much sur- 
vive, and by natural selection wingless breeds or species are 
produced. Finally, we may mention the great modifications 
of structure, often resulting in the loss of certain organs, 
which take place to produce protective resemblances (see 
Chapter XII). In such cases the body may be modified in 
14 
