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 
passes into the chrysalis stage, and later on 
emerges as a perfect insect. Here, among the 
vertebrates, we 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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