LIFE-HISTORY OF A FROG 



i, Before hatching; 2, newly hatched larvce hanging on to water-weed; 3, with external 

 gills; 4, external gills are covered over and are absorbed; 5, limbless larva about a month 

 old with internal gills; 6, tadpole with hind-legs, about two months old; 7, with the fore- 

 limbs emerging ; 8 , with all four legs free ; 9 , a young frog , about three months old , showing 

 the almost complete absorption of the tail and the change of the tadpole mouth into a frog 

 mouth. 



Photo: J. J. Ward, F.E.S. 



HIND-LEG OF WHIRLIGIG BEETLE WHICH HAS BECOME 



BEAUTIFULLY MODIFIED FOR AQUATIC LOCOMOTION 



The flattened tips form an expanding "fan" or paddle, 

 which opens and closes with astonishing rapidity. The closing 

 of the "fan," like the "feathering" of an oar, reduces frictioa 

 when the leg is being moved forwards for the next stroke. 



