RUDIMENTARY ORGANS. 287 
seeing. But as the animals gradually accustomed them- 
selves to an underground mode of life, and withdrew from 
the daylight and no longer used their eyes, these became 
degenerated. 
Very clear examples of rudimentary organs, moreover, are 
the wings of animals which cannot fly; for example, the 
wings of the running birds, like the ostrich, emeu, casso- 
wary, etc, the legs of which have become exceedingly 
developed. These birds having lost the habit of flying, have 
consequently lost the use of their wings; however, the 
wings are still there, although in a crippled form. We very 
frequently find such crippled wings in the class of insects, 
most members of which can fly. 
From reasons derived from comparative anatomy and 
other circumstances, we can with certainty draw the 
inference that all insects now living (all dragon-flies, grass- 
hoppers, beetles, bees, bugs, flies, butterflies, etc.) have 
originated from a single common parental form, from a 
primary insect which possessed two well-developed pairs 
of wings, and three pairs of legs. Yet there are very many 
insects in which either one or both pairs of wings have 
become more or less degenerated, and many in which they 
have even completely disappeared. For example, in the whole 
order of flies, or Diptera, the hinder pair of wings—in the 
bee-parasites, or Strepsiptera, on the other hand, the fore pair 
of wings—have become degenerated or entirely disappeared. 
Moreover, in every order of insects we find individual 
genera, or species, in which the wings have more or less 
degenerated or disappeared. The latter is the case espe- 
cially in parasites. The females have frequently no wings, 
whereas the males have; for instance, in the case of glow- 
