SURVEY OF VERTEBRATES 



115 



2. Bony Fishes 



All of the fresh-water Fishes, as well as the great majority of 

 those dwelling in the sea — indeed, what we usually think of as 

 Fishes — typically have a skeleton of 

 bone, and a body-covering of scales. 

 They are Bony Fishes, or Teleosts. 

 True, the more primitive forms have 

 partially cartilaginous skeletons, and 

 bony plates instead of scales, as rep- 

 resented by the Garpikes and Stur- 

 geons, but they are exceptions form- 

 ing less than five per cent of the 

 group. All Teleosts have the external 

 openings of the gill slits covered by a 

 protecting flap, or operculum, so that 

 water bathing the gills leaves the body 

 by a single opening at the posterior 

 edge of the operculum on either side of 

 the head. (Figs. 71, 100, 106.) 



Modifications of the typical fish-like 

 r « .«. . . T7i. i ., Fig. 72. — Sea-horse, Hip- 



form of swift-swimming Fishes that pocampus antiquorum . Ma le 



have been assumed by various species showing brood pouch formed 



in adaptation to different habitats and from combined pelvic fins. 

 i p it l r\ (From Doflein.) 



modes ot hie are legion. One imme- 

 diately thinks of the snake-like body of the Eels, the grotesque 

 form of the Sea-horses, and the compressed body of the Flat- 

 fishes, such as the Flounders and Halibuts. But Flat-fishes are 



hatched with typical fish 

 form; and it is only as 

 the animals settle down 

 on one side that the 'un- 

 der' eye moves up and 

 over so both are on top. 

 Even the bizarre form ex- 

 hibited by the Flying- 

 fishes that jump and sail 

 above the water is exceeded by the denizens of the ocean's deepest 

 reaches, where sunlight never penetrates, no plant life grows, 

 the pressure is tremendous, and the temperature is only slightly 



Fig. 73. — A Flat-fish. 



