16 LECTURES ON BIOLOGY 



with widely extended breast-fins from the water and are car- 

 ried in a direction opposite to that of the wind and kept 

 suspended for some distance by the current which is caught 

 under the wing-like fins. It is also probable that they assist 

 their flight by an up-and-down movement of the breast-fins. It 

 seems that the flying-fishes use their ability chiefly for escaping 

 from their numerous enemies among the fishes of prey, often 

 only to fare worse. For no sooner has a swarm of gurnards 

 risen than it is attacked by the ever-ravenous sea-gulls. Some- 

 times they rise in the air in play, like our trout, which on fine 

 summer evenings leap from the water with audacious jumps. 

 : In the seas of the Tropics the flying-fishes are still more 

 common. As soon as a ship has passed the Equator it is during 

 fine weather accompanied by shoals of these curious creatures. 

 There are in all more than fifty species of flying-fishes, of 

 which the Swallow-fish (Exoccztus volitans), an inhabitant of 

 the Mediterranean, is most widely known next to the Flying 

 Gurnard. 



Whilst the extremities, and m particular the paired pectoral 

 fins, of the flying-fishes have developed to large dimensions, we 

 know on the other hand numerous species in which the fins 

 have degenerated into small insignificant forms which are of little 

 use in locomotion. All such fishes I will only mention eels, 

 murcence, ribbon-fishes and needle -fishes are distinguished by a 

 striking elongation of the body-axis. This phenomenon may be 

 easily explained, with Lamarck, as a result of use and disuse. 

 When body and tail are growing longer they commence to 

 participate in the locomotion by snake-like twists and turns, 

 thus tending more and more to relieve the extremities ; when the 

 elongation of the axis becomes extreme, the extremities cease 

 to be active and consequently become degenerate. 



All that is said here of the fishes is equally applicable to the 

 higher classes of the vertebrates. The short, tailless frogs have 

 very strong legs which are equally well adapted to swimming, 

 jumping, and climbing. In the long-tailed salamanders and newts 

 the extremities are less strongly developed ; in the Amphiuma 

 (A. means), and still more so in the snake-like Csecilians 

 (Gymnophiona) , they become rudimentary or disappear altogether- 

 The same observation applies to the reptiles. Tortoises, lizards, 



