XIII LOCOMOTION 355 
action of the median fins in swimming must be regarded as 
supplementary to that of the tail. 
Swimming is by no means the only form of locomotion in 
vogcue amongst Fishes. A few, like the Angler-Fishes (Lophius), 
habitually use the pectoral fins for crawling about the sea-bottom. 
The East Indian Goby, Periophthalmus, uses its pectoral fins, 
which are bent at an angle like an elbow-joint, for hopping over 
sandy flats left bare by the retreating tide. The Flying-Fish 
(Exocoetus), when projected from the water by a stroke of its 
powerful tail, expands its large pectoral fins, and, using them 
after the fashion of a parachute, floats through the air for con- 
siderable distances before returning to its natural medium. The 
“Flying Gurnards” (Dactylopterus) are also capable of short 
aerial excursions in a similar fashion. Nor is tree-climbing 
beyond the province of a Fish, if credit be given to the assertion 
that the Indian “Clmbing-Perch” (Anabas scandens) uses its 
opercular spines for ascending trees. Many freshwater Fishes 
are known to migrate across land from one pool or river to 
another, usually during the night. Eels do so by a serpentine 
or wriggling motion of their long bodies, but in others the 
pectoral fins seem to be the principal organs used for the 
purpose, aided, it may be, by a perverted use of the tail. 
Sound-producing Organs.—Contrary to popular belief sound- 
producing or vocal organs are by no means uncommon in Fishes, 
especially in certain families of Teleosts. It is not always easy, 
however, to discriminate between involuntary, abnormal, or acci- 
dental sounds, and those due to the action of special vocal organs. 
There are, moreover, some Fishes which observations have shown 
to utter highly characteristic sounds, although the precise nature 
of the sound-producing mechanism is at present unknown; while 
other Fishes appear to possess organs which, on anatomical 
srounds, are perhaps vocal in function, although nothing is 
known of the nature of the sounds they emit. Here those 
organs only will be considered which, either with certainty or 
with some degree of probability, may be regarded as vocal struc- 
tures. For most of our knowledge of these interesting structures 
we are indebted to the researches of Sorensen and Dufossé.’ 
1 Sérensen, Om Lydorganer hos Fiske, Copenhagen, 1884 ; Dufossé, Ann. d. 
Sci. Nat. Sér. 5, xix. Art. 5, 1874, and xx. Art. 38, 1874. For references to earlier 
papers see Sorensen, op. cit. 
