AMPHIBIANS 2623 



Amphibians pass through a metamorphosis, or rather a series of metamorphoses, 

 commencing their existence immediately after leaving the egg in a larval condition, 

 during which they breathe the air contained in water by means of gills, while in the 

 adult state they breathe atmospheric air by means of lungs. Varying much in ex- 

 ternal form, these animals nearly always have the body covered with a soft naked 

 skin; but in a few instances among existing forms scales are imbedded in the skin, 

 and most of the extinct forms had a well-developed armor of scales and bony scutes. 

 In some forms a longitudinal fin is developed down the middle of the back and tail, 

 but this is always soft, and lacks the supporting spiuous bones characterizing that 

 appendage in fishes. In passing through a metamorphosis, Amphibians are more 

 like the inferior groups of animals than the higher Vertebrates; and while in the 

 earlier stages of their existence, during which they breathe by gills, they may be 

 regarded as very closely allied to Fishes, in the adult state they come much nearer 

 to Reptiles. The extinct L,abyrinthodonts, which are themselves not very widely 

 removed from fishes, and have the basioccipital bone, ossified, serve to connect 

 other members'of the class with the Anomodont and Beaked Reptiles. And it may 

 be mentioned here that while in Mammals the skull has continued to be supported 

 by the two condyles of the Amphibians, in the Reptiles the basioccipital bone 

 has developed an intermediate condyle filling up the gap between the two exoc- 

 cipital condyles, and thus forms a single tripartite condyle like that of the tor- 

 toises. Frequently, as in the crocodiles, the lateral elements have tended more or 

 less completely to disappear, thus leaving a condyle formed almost entirely by the 

 basioccipatal. 



As already said, the skin of most existing Amphibians is soft and 

 naked; it is invested with a colorless epidermis, which is periodically 

 shed entire, while the deeper layer is often colored with blotches or streaks of yel- 

 low, red, brown, or black. Other colors, however, such as green and blue, are pro- 

 duced by pigment cells, which generally make their appearance under special 

 conditions of warmth and moisture. As a rule, the color of Amphibians varies to a 

 great extent with the nature of their surroundings, as is well exemplified in the case 

 of the frog, which changes its hue according to the nature of its habitat; while the 

 tree frogs harmonize with the foliage among which they dwell. It is, however, 

 very remarkable that in Costa Rica a certain toad simulates to an extraordinary de- 

 gree the coloration of the snakes both poisonous and harmless of the same 

 country; while in North Sumatra Amphibians of various groups are spotted with 

 carmine red. In all Amphibians the skin is furnished with glands secreting a more 

 or less milk-like fluid; these glands being generally distributed all over the body, al- 

 though sometimes they are confined to the sides of the neck behind the eyes. In 

 many toads and land salamanders some of the larger glands appear as prominent 

 warts, pierced with large pores. The viscid, milky fluid secreted by these glands 

 is exuded during excitement, and is endued with more or less poisonous properties, 

 being intended to serve as a means of defense. Although some degree of irritation 

 of the skin may be produced by handling some of the species in which these poi- 

 sonous properties are most developed, the stories of toads or salamanders spitting 

 venom are, it is almost needless to observe, pure fabrications. When introduced 



