48 ANIMAL LIFE 



our coasts have a relative on Eastern shores that hops 

 with great vigour on its front fins, keeping its tail 

 in water. A perch with the same implements manages 

 to shuffle up overhanging boughs, and the bat-fish 

 has actually developed an elbow-joint, whereby it 

 can rest its weight on the flat part of the fin. But 

 no amount of ingenuity has conferred on any fish we 

 know the ability to walk freely. 



On the other hand, at least two groups of the 

 most active swimming fish have developed that power 

 of leaping into the air, often found in the most varied 

 groups, into a sustained, gliding movement which 

 resembles flight. For this purpose the flying-fish 

 employ their powerful breast fins, which they keep 

 spread out like a parachute. By the aid of this 

 aeroplane their descent is delayed ; and so powerful 

 is the initial jump from the sea into the air that, with 

 a favouring breeze, they may rise on to the deck of a 

 steamer or go clean over a fishing-boat. 



II. The adaptations of terrestrial vertebrates. — It is, 

 however, only when we ascend above fish to the 

 higher vertebrates that we find the problems of move- 

 ment on land and in the air completely solved. 



On land, weight enters into the problem. Support, 

 unneeded in the sustaining water, becomes now a 

 necessity ; and in order that this weight may be 

 upborne and moved, all the skeletal parts require to 

 be denser, both on account of the vertical strain they 

 support and the greater muscular tension requisite 

 for movement. The limbs become props whilst 



