ADAPTATIONS 377 



habitual mode of life the tail-fin, which is richly furnished with 

 blood-vessels, serves as an accessory organ of respiration. 

 Periophthalmus australis is common on the shores of Queens- 

 land and grows to a length of twelve inches. In the various 

 families of anglers, forming the sub-order Pediculati, the pec- 

 torals are modified for use as limbs rather than as fins, none of 

 these fishes swimming freely in the water. The bones at the 

 base of the fin are reduced to two or three in number and 

 greatly lengthened, so as to resemble the bones of the fore- 

 limb (radius and ulna) of a terrestrial vertebrate, and they form 

 a kind of wrist joint with the broad part of the fin. In the 

 angler and other forms which live on the bottom, they are 

 used for shuffling along the ground. The pelvic fins are simi- 

 larly modified, and indeed these are really more to be compared 

 to fore-limbs, for they are situated in front of the pectorals and 

 nearer to the middle of the ventral surface. The resemblance 

 in attitude and locomotion to a frog or toad is greatest in the 

 Malthidae, e.g. Malthe vespertilio, in the West Indies. 



The family of pipe-fishes, placed in classification in 

 the same sub-order as the familiar sticklebacks, offers some 

 striking examples of adaptation for concealment, or as it is 

 technically termed protective resemblance. These fishes all 

 live among sea-weed, and their slender stiff bodies, usually pro- 

 tected by bony scutes in the skin instead of scales, have more 

 or less resemblance in colour and shape to fronds of the weeds. 

 Thus one of the British species is bright green and in shape as 

 well as colour is very similar to the blades of the sea-grass 

 among which it is always found. The well-known sea-horse, 

 Hippocampus, like the pipe-fishes, swims vertically and has a 

 prehensile tail which he curls round stems of sea-weed. In an 

 Australian sea-horse, Phyllopteryx eques, the resemblance is 

 carried to a remarkable degree by the presence of branched 

 flat appendages of the skin which have the same appearance 

 as the fronds of sea-weed. Another extraordinary fish of this 

 group is Ampkistle, which lives on the coasts of the Indian and 

 Pacific Oceans. This fish is almost as narrow from side to 

 side as a knife-blade : the plates of the skin are united with 

 the internal skeleton as in a tortoise: the small tail-fin is 

 bent round to the ventral side, and the dorsal fins are at the 

 end of the body. The fish swims vertically with its head 



