Outlines of zoology . Fig. 5.—Salamander, an Amphibian. among Fishes, to terrestrial life, habitual among Reptiles;for while almost all Amphibians have gills—in their youthat least—all the adults have lungs, and some retain the gillsas well. In having limbs which are fingered and toed, andthus very different from fins, they resemble Reptiles. Butthe two foetal membranes characteristic of the embryonic lifeof higher Vertebrates are not present in Amphibian embryos,and the general absence of an exoskeleton in modern formsis noteworthy. Fishes.—The members of this class are as markedlyadapted to
Outlines of zoology . Fig. 5.—Salamander, an Amphibian. among Fishes, to terrestrial life, habitual among Reptiles;for while almost all Amphibians have gills—in their youthat least—all the adults have lungs, and some retain the gillsas well. In having limbs which are fingered and toed, andthus very different from fins, they resemble Reptiles. Butthe two foetal membranes characteristic of the embryonic lifeof higher Vertebrates are not present in Amphibian embryos,and the general absence of an exoskeleton in modern formsis noteworthy. Fishes.—The members of this class are as markedlyadapted to life in the water as birds to life in the air. Thevery muscular posterior region of the body usually forms. Fig. 6.—Queensland dipnoan (Ceraiodus). the locomotor organ, and we say that a fish swims bybending and straightening its tail. The limbs have theform of paired fins—that is, they are limbs without are also unpaired median fins supported by fin have permanent gills borne by bony or gristly arches. 6 GENERAL SURVEY OF THE ANIMAL KINGDOM. There is an exoskeleton of scales, and the skin also bearsnumerous glandular cells and sensory structures. In many ways Fishes are allied to Amphibians, especiallyif we include among Fishes three peculiar forms, known asDipnoi, which show the beginning of a three-chamberedheart, and have a lung as well as gills. Ordinary Fisheshave a two-chambered heart, containing only impure blood,which is driven to the gills, whence, purified, it passesdirectly to the body. Apart from the divergent Dipnoi, there are two great orders ofFishes—the cartilaginous Elasmobranchs, such as shark and skate ;and the Teleosteans or bony fishes, such
Size: 3166px × 789px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookdecade1910, bookidcu3192, booksubjectzoology
