EUDIMENTARY OUGANS. 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- 



