CHAMBERS'S INFORMATION FOR THE PEOPLE. 



CLASS II. AMPHIBIA. 



This class was included by Cuvier along with 

 the Reptiles, but there is sufficient reason for 

 separating them into a distinct group of equal 

 importance. They may be regarded as inter- 

 mediate in their structure and in their habits and 

 mode of life, as well as in many of their forms, 

 between Fishes and true Reptiles. To the former 

 they are allied, in that at some period of their 

 life they breathe by gills, but differ from them in 

 always possessing lungs in the adult condition. 

 Their limbs are never in the form of fins. The 

 skull articulates with the vertebral column by two 

 occipital condyles, and the heart consists of two 

 auricles and a single ventricle. From the arterial 

 and venous blood being mixed in the ventricle, 

 the body is nourished by imperfectly oxygenated 

 blood. They are, like Fishes and Reptiles, cold- 

 blooded animals. They all undergo a metamor- 

 phosis after their expulsion from the egg. At 

 first, they possess gills, and are water-breathing 

 animals ; but in the adult state they invariably 

 possess lungs. In some genera, the gills dis- 

 appear as the lungs are developed ; but in other 

 cases, both gills and lungs are permanently retained 

 throughout life. As in Reptiles, the gut, and the 

 ducts from the kidneys and generative organs, 

 open into a common cloaca. 



ORDER i. Ophiomorpha (serpent-forms) in- 

 cluding one genus, the Cacilia, Blind Newt, or 

 Naked Serpent It is snake-like in form, and 

 destitute of limbs. The eyes are exceedingly 

 small, and are nearly hidden under the skin. It 

 is a native of South America, Guinea, and Ceylon. 



ORDER 2. Urodela, or Tailed Amphibians. 

 The animals included under this group retain 

 their tails in the adult condition, and their skin 

 is soft, and destitute of scales. In one section 

 (Amphipneusta), both gills and lungs are re- 

 tained throughout life for example, the Proteus 

 of the caves of Illyria, and the Siren or Mud-eel 

 of the rice-swamps of South Carolina. In the 

 second section, the gills disappear at maturity, 

 and the animals breathe by lungs alone. This 

 section includes the Land and Water Salaman- 

 ders. The Tritons, or Aquatic Salamanders, 



Warty -newt (Triton cristatus). 



commonly called Newts, have their tail verti- 

 cally compressed, and are oviparous. They 

 pass the greater part of their life in the water. 

 They possess the remarkable power of repro- 

 ducing limbs that have been cut off. The 



162 



anterior limbs are developed first in the Sala- 

 manders, the reverse of what takes place amongst 

 the frogs. Three species are indigenous to 

 Great Britain. The Land Salamanders (Sala- 

 mandra) are distinguished from the former by the 

 cylindrical form of their tail, and by their pro- 

 ducing their young alive. All these forms are 

 easily distinguished from the Reptiles by always 

 possessing gills at the earlier period of their life, 

 and by the soft, smooth, naked skin. 



ORDER 3. The Anoura, or Tail-less Am- 

 phibians, including the Frogs and Toads. The 

 adult is destitute of both gills and tail, both of 

 which structures exist in the larva. Four limbs 

 are always present. The larvae are known as 

 ' tadpoles,' which have a round head, a fish-like 

 tail, and breathe by gills. Ultimately, the tail 

 disappears, limbs are budded forth (the posterior 

 pair first), and the gills are replaced by lungs, so 

 that the adult is an air-breathing animaL 



Family Ranidcz, or Frogs (rana, a frog). They 

 are so well known that a description of them 

 seems unnecessary. They always possess teeth 

 in the upper jaw. They are of a yellowish-brown 

 colour, with black spots, and their power of leaping 

 is well known. As there are no movable ribs to 

 expand the thorax, the mode of breathing is pecu- 

 liar. The animal closes its mouth, and fills it 

 with air taken in through the nostrils ; the nostrils 

 are then closed, and by the compression of the 

 muscles of the throat and cheeks, the air is pro- 

 pelled forcibly into the lungs. The animal would 

 be choked if the mouth was held open. No doubt, 

 the skin also aids in the process of respiration. 

 Their feet are webbed, and suited for swimming. 

 Of the European species, the Edible Frog (A'. 

 esculenta) is the one most approved of on the 

 continent for culinary purposes. The R. tem- 

 poraria is the only species indigenous to Britain. 

 The Tree-frogs (Hylce] of America have their 

 feet provided with suckers, which enable them to 

 climb trees in pursuit of their food insects. 



Family Pipida, distinguished by the absence of 

 the tongue, including the ugly Pipa Americana, or 

 Surinam Toad, which is eight inches long in the 

 tadpole condition, while the perfect frog is only 

 three in length. It is a native of Brazil and 

 Surinam. 



Family Bufonid<z (Toads) in which the jaws are 

 destitute of teeth. They are of a dull, cadaverous 

 appearance, and their bodies are covered with 

 warts. They have a swelling above each eye, 

 from which a fetid, milky secretion is expressed. 

 Two species are found in Britain, the Common 

 Toad (Bufo vulgaris), and the Natterjack (B. 

 calamita). They seldom frequent the water but 

 for the purpose of depositing their eggs. The 

 tongue in these animals, as in the frogs, is fixed 

 to the front of the mouth, and free behind. 



CLASS III. REPTILIA. 



The Reptilia, or creeping animals (repo, I creep), 

 though in outward form many of them resemble 

 the Amphibia, yet in intimate structure they are 

 more closely allied to birds. They are oviparous, 

 and many of them are covered by hard scales, but 

 never by feathers. They never breathe by gills, 

 but always by lungs. The heart consists of two 

 auricles and a ventricle, so that only a portion 

 of the blood returned by the veins is propelled 



