TO AQUATIC LIFE. 61 



in man. But what would have been tlie result if both 

 arm and forearm had extended freely from the side of the 

 fish, and dangled as a long many-jointed appendage in 

 the water ! This " higher development," as it is termed, 

 in relation to the prehensile or cursorial limb of the deni- 

 zen of dry land, would have been a defect in the structure 

 of a creature destined to cleave the liquid element. In 

 the fish, therefore, the fore -limb is left as short as was 

 compatible with its required functions ; the broad man}^- 

 fingered hand alone projects, but can be applied prone 

 and flat, by flexion of the wrist, to the side of the trunk ; 

 or it may be extended with its flat surfaces turned forwards 

 and backwards, so as to check and arrest, more or less 

 suddenly, the progress of the fish ; its breadth can also 

 be diminished by closing up or stretching out the digital 

 rays. In the act of flexion, the pectoral fin slightly ro- 

 tates, and gives an oblique stroke to the water. The 

 requisite breadth of the modified hand is gained by the 

 addition of ten, twenty, or it may be a hundred fingers 

 oyer and above the number to which they are restricted 

 in the forefoot or hand of the higher classes of vertebrata. 

 The pike maintains a stationary position in a stream by 

 vibrations of the pectoral fins ; the nature of the bottom of 

 the fish's habitat is ascertained by a tactile application of 

 the same fins. In the hard-faced gurnards, certain rays 

 of the pectorals are liberated from the web, and have a 

 special endowment of nerves, in order to act as feelers. 

 In the siluroid fishes, the pectorals wield a formidable 

 weapon of offence. A tropical species of perch {Anahas) 

 uses a smaller analogous pectoral spine for climbing up 

 the mangrove stems in quest of insects. 



Certain lophioid fishes, that live on sand-banks left dry 

 at low water, are enabled to hop after the retreating tide 

 6 



