134 THE WEALTH OF THE SEA 



wanting in some of the flatfishes (soles), but are 

 present in a variety of shapes and forms in other 

 fishes. In the skates and rays they form a very broad 

 wing-like fleshy expansion. In the flying fishes these 

 fins are also long and broad but not fleshy, resem- 

 bling the wings of birds. As a matter of fact they 

 are used in a measure as wings, for the flying fishes 

 are capable of "flying" a distance of a hundred yards 

 or so. The "wings" in these fishes, however, are not 

 capable of movements like the wings of a bird; all 

 the momentum is gained in the water, principally by 

 the tail fin supported by powerful muscles, the 

 shoulder fins merely aiding the fish to stay in the air 

 after it has made its powerful leap, just as the 

 motionless expanded wings of a bird keep it from 

 falling directly to the earth. 



All the other fins, likewise, are subject to great 

 variations. The tail fin is forked in some species, 

 round or pointed in others, with all manner of inter- 

 mediate shapes. This fin quite probably is the chief 

 organ of propulsion, whereas the other fins more 

 nearly serve the purpose of balancing organs. In 

 the top-minnows which give birth to live young, the 

 fin situated just behind the vent has a peculiar 

 connection with sex, for in the adult male it is always 

 modified and serves as an intromittent organ in 

 conveying the sperms from the male to the female. 

 The top-minnow now commonly known as Gambusia, 

 widely used for destroying the immature mosquito, 

 which lives in the water, belongs to this interesting 

 group of little fishes. 



The fins in fishes, unlike the arms and legs of 



