GREY MULLETS— THREAD-FINS— PARASITIC FISHES 



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•movements as take place in the wings of flying-gurnards are similar in their nature 



to the vibrations which are admitted to occur in those of the flying-herrings or true 



flying-fishes. This author summarises the whole case by stating that it may be 



taken as certain that the initial impetus by means of which flying-fishes of both 



kinds launch themselves is due to powerful screw-like movements of the tail-fin. 



The wings are in no sense propelling organs, but act simply as parachutes. 



This opinion has been disputed by an English writer, who maintains that the 



ordinary ' aeroplane-theory ' of the flight of these fishes is based on an absolute 



mechanical impossibility, and that the real explanation is to be found in intensely 



rapid vibrations of the wing-like pectoral fins — vibrations which are revealed to 



the eye when the movement slows down as the fish touches the crest of a wave. 



Another family of the Percesoces is formed by the well-known 

 Grey Mullets. . J 



grey mullets, Mugifoaaz, so highly esteemed as food-fishes. These 



form a widely distributed group, chiefly characteristic of temperate and tropical 



seas, although a few frequent brackish waters. Among them, the common grey 



mullet (Mugil capito) ranges from the North Sea to the Cape of Good Hope. 



Nearly allied are the members of the family Polynemidce, as 

 represented by Polynemus and two other genera. These fishes are 

 •characterised by bearing a tuft of whip-like appendages a short distance in front 

 of and below each pectoral fin. They inhabit the shores of tropical seas, and 

 frequently enter estuaries in the muddy waters of which the long, freely movable 

 pectoral fins apparently serve as organs of touch ; and it is probabty by their aid 

 that these fishes are enabled to find their way and obtain their food. The second 

 genus is represented by Pentanemus quinquarius, in which the pectoral append- 

 ages exceed the body in length. Some of these thread-fins attain a length of four 

 feet, and they are all valued alike as food, and for the isinglass yielded by their 

 air-bladders. 



Another family of the same group, the Sphyrcenidce, includes 



153,12(1,0 UC13.S . w m 



the large, elongated, subcylmdrical fishes of voracious habit 

 commonly known as barracudas, all of which are furnished with a series of power- 

 ful conical teeth. There are nearly a score of species, among w T hich the ordinary 

 barracuda (Sphyrcena vulgaris) of the Mediterranean grows to four feet, but some 

 of the other kinds attain double this length. 



In a different group the curious little fishes of the family Fieras- 



jeridie, especially of the genus Fierasfer, are of interest on account 

 •of their habit of infesting the breathing-chambers of sea-cucumbers, or holothurians, 

 and other invertebrates, where they subsist on such organisms as come within their 

 reach. Beyond sharing the food-supply, they appear, as a rule, to do no damage 

 rto their involuntary hosts ; but one species, F. vermicular is, in its larval state at 

 all events (when it has no pectoral fins), has been stated to feed on the viscera of 

 the holothurians in which it takes up its abode. The family includes about half a 

 score of small species, distributed over the Pacific, Indian, and Atlantic Oceans, and 

 .also entering the Mediterranean. An American naturalist has described the manner 

 in which F. ajjinis effects an entrance into the body of the sea-cucumber, 

 which serves as its host. When the small pellucid fish comes alongside of the holo- 

 thurian, it gradually feels its way down the body of the latter by means of its head 



