USE AND DISUSE OF ORGANS. 185 



motive apparatus. A general reduction, of the power 

 of flight has been shown in the beetle fauna of many 

 islands. Thus in Madeira, of 550 species, over 200 fly 

 imperfectly or not at all, and for this there is no ex- 

 planation but natural selection. Here the less good 

 and enterprising flyers had the advantage, while the 

 others were blown into the sea and eliminated. The 

 non-application of a previously attained special per- 

 fection is advantageous in the " struggle for exist- 

 ence."' 



In several families of lizards, some genera are ser- 

 pentine, as they are termed, which, with elongated bodies, 

 possess either fore-legs only (Chirotes), or merely rudi- 

 mentary hind-legs (Pseudopus), or no vestiges of legs 

 (Anguis). They bear the same relation to the great class 

 of normally four-legged lizards as the non-flying insects 

 to their own class. They have not been arrested in their 

 development, nor are they animals in process of evolv- 

 ing four legs; but, as Fiirbringer has demon.strated from 

 the history of development and comparative anatomy, 

 their limbs, and — if these are entirely absent — the remains 

 of the pectoral and pelvic arches and the sternum bear 

 indubitable marks of the abortion of a once complete 

 apparatus. Further comparison shows that this atrophy 

 reaches its climax in the snakes, but that it is compen- 

 sated for by the ribs and intercostal muscles having un- 

 dertaken the work of the limbs. Here, again, disuse and 

 adaptation coincide as well as diflferentiation. 



In the class of birds is repeated the spectacle we have 

 just witnessed in beetles and reptiles. In some few 

 families and smaller groups, individual species are de- 

 prived of the power of flight, and one whole large sys- 



