376 FISHES 



reversed, the ventral surface is dark brown the dorsal a light 

 silvery grey. The peculiar habit attracted the notice of the 

 ancient Egyptians who have represented the fish frequently in 

 this unusual position. By the expression " distribution of pig- 

 ment " used above is meant the presence of pigment on one part 

 and its absence on another ; the cause of the particular colours 

 and markings such as spots and stripes in various patterns which 

 are so conspicuous in some fishes is another question which is 

 much more difficult to answer. The reason for the inverted 

 position assumed by Synodontis seems to be unknown, but it 

 may at least be said that the diminution of pigment on the 

 dorsal side, which becomes the lower in the inverted position, 

 is not known to be of any benefit to the fish. 



The most remarkable adaptation for locomotion among 

 fishes is that of the pectoral, and to some extent the pelvic fins 

 also, in the flying-fishes. In Exocoetus and its allies the pectorals 

 are enormously enlarged, and lengthened, extending back to 

 within a short distance of the tail. In Dactylopteridse, the fly- 

 ing gurnards, the pectorals are even longer in proportion to the 

 body. In the former the fins are used as parachutes, not being 

 vibrated during the flight, but in the latter they are stated by ob- 

 servers to be moved rapidly up and down like the wings of a 

 butterfly. Recently a fresh-water flying-fish belonging to a 

 totally distinct family has been discovered in the Congo region, 

 namely Pantodon buchholtzii, belonging to the soft-finned sub- 

 order Malacopterygii. The pectorals in this case are not so 

 much elongated, but they are united to the body by membrane, 

 and the pelvic fin-rays are separate and elongated as filaments ; 

 this little fish is only three and a half inches long, and was 

 taken in its flight over the water by a butterfly net. Among 

 the Gobies, the mud-skippers of tropical shores are adapted for 

 hopping about the surface of the mud, using their pectorals, of 

 which the bases are very muscular, as short legs. The head 

 is raised on the pectorals in an attitude resembling that of the 

 frog, and the eyes project upwards from the head, and are 

 capable of free movement, whence the names Periophthalmus 

 and Boleophthalmus given to the genera. They not only hop 

 actively on the mud but climb on to mangrove roots, and move 

 so quickly that it is difficult to catch them. They are unable 

 to live under water more than a limited time, and in their 



