CHAPTER XL 



INTRODUCTION TO THE CLASS OF AMPHIBIANS 



Among the many wonders of Nature, few are 

 more interesting to the thoughtful mind than 

 those forms which connect the great groups of 

 vertebrate animals by bridging over what other- 

 wise would seem like impassable chasms. 



For example, between the classes of Mammals 

 and Birds we have the Platypus, or Duck-Bill, 

 an Australian mammal the size of a small musk- 

 rat, which has webbed feet, and a duck-like bill, 

 and which reproduces by laying eggs. Between 

 the classes of Birds and Reptiles, there is a fossil 

 bird called the Ar-chae-op'-te-ryx, with a long, 

 vertebrated, lizard-like tail, covered with feath- 

 ers. The Hes-per-or'nis was a water-bird with 

 teeth, but no wings, which inhabited the shores 

 of a great western lake which now is a vast 

 stretch of arid bad-lands. 



Between the Reptiles and the Fishes stretches 

 a wonderful chain of living links by means of 

 which those two Classes are united. So numer- 

 ous are these forms, they make an independent 

 Class, containing about 1,040 species. Originally 

 this group was called Ba-tra' chi-a , but recently 

 the fact has been recognized that that term is 

 too limited in its application, and by the latest 

 authorities the term Am-phib'-i-a has been 

 adopted instead. 



In the transition from the water-habiting 

 Fishes, with gills and fins, to the land-going Rep- 

 tiles, with lungs and legs, Nature has made some 

 strange combinations. In some instances, fins, 

 legs, lungs and gills have become so mixed that 

 several notable misfits have resulted. In some 

 cases we see legs going with gills, and in others 

 fins and lungs are associated. Many of the Am- 

 phibians will serve teachers as very striking 

 object lessons in the evolution of animal forms. 



The Class Amphibia contains the cold-blooded 

 vertebrates known as frogs, toads, salamanders, 

 newts, proteans, and sirens. 



In the insect-world, we are familiar with the 

 three stages of existence by which the larva 



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passes into the chrysalis stage, and later on 

 emerges as a perfect insect. Here, among the 

 vertebrates, wc find creatures which also pass 

 through two very distinct and sharply defined 

 stages. 



An Amphibian, if literally translated from 

 the Greek, is a creature of "two lives." A typi- 

 cal amphibian begins life as a legless, fish-like 

 creature, possessed of perfect gills, an eel-like 

 tail, and living wholly in water. This is the 

 larval stage of the animal. Later on, four legs 

 make their appearance, the tail disappears by 

 absorption into the body, the digestive organs 

 change from simple to complex form, and lungs 

 take the place of gills. In this adult stage, the 

 creature (usually) is fitted for life on land if it so 

 elects. 



Owing to the bewildering variations of form 

 and anatomy that are exhibited by various spe- 

 cies, it is almost impossible to formulate a gen- 

 eral statement regarding amphibians which will 

 not be open to exceptions. If the reader will 

 bear this in mind, we may venture to state the 

 leading characters of the members of this Class. 



General Characters. — All save a very few 

 amphibians are hatched from soft, translucent, 

 jelly-like eggs that are laid in shallow water, 

 usually in stringy masses. Sometimes the larval 

 stage of a species is passed in the egg, but usually 

 this period forms an important part of the active 

 life of the animal, and may be observed at length 

 before the change to the adult stage takes place. 

 Amphibians are (usually) covered with smooth 

 skins, quite destitute of scales, and have minute 

 teeth, or none at all. During the larval stage 

 they feed chiefly upon vegetable food, but when 

 adult the majority require animal food. Their 

 skeletons are much more simple in structure than 

 those of reptiles. The majority are aquatic. 

 Some species permanently retain their gills, and 

 live wholly in water; others, like the frogs and 

 toads, lose their gills, acquire practical lungs and 

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