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CLASS AMPHIBIA. 



State the general Features of Amphibians. 



The skin is generally scaleless. The unpaired fins, when 

 present, are without fin-rays.* The limbs, when present, 

 are pentadactyle.* (See page 194.) The skull (autostylic) 

 has two occipital condyles. The olfactory sacs open into 

 the front of the mouth by internal nares. There is a middle 

 ear, with one ossicle (the columella*). There are lateral 

 line sense organs in the larva, and in certain adult Am- 

 phibians. The gut, and the renal and genital ducts open 

 into a cloaca. A ventral outgrowth of the rectum (the 

 allantois) functions as a urinary cloacal bladder.* Gills, 

 present as a rule in the larva, may remain functional 

 throughout life ; but normally the adults breathe by lungs. 

 The heart consists of a sinus venosus, two auricles, a ventricle, 

 and a conus. There is a renal portal and a hepatic portal 

 system. The eggs, small and numerous, are laid usually 

 in water ; and segmentation is total (holoblastic), but un- 

 equal. Metamorphosis is generally a feature of the life- 

 history. 



Mention the Principal Features which distinguish Amphi- 

 bians from Fishes. 



Those marked * in preceding answer. 



Classify the Amphibia, and give Examples. 

 Order URODELA or CATJDATA. Tailed throughout life. 



Examples, Amphiuma. Limbs rudimentary. Teeth on 



upper and lower jaws. Adult without gills. 

 Siren. Hind limbs absent. Toothless. Adult 

 with gills. 



Triton (Newt). Limbs well developed. Teeth 

 on upper and lower jaws. Gill-clefts and 

 gills absent in adult. Generally oviparous. 



Salamandra. Viviparous. 8. atra " lives at ele- 

 vations (Alps) where water-pools are rare," 

 and the young are born without gills (adapta- 

 tion to environment). 



Amblystoma or Siredon. Without gills. Its 

 gilled larva, known as the axolotl, frequently 

 breeds (paedogenesis, see Part II., page 95). 



