AMPHIBIANS 
(Worm-like Amphibians, Salamanders and Newts, Frogs and Toads) 
Hundreds of thousands of years ago, in the steamy humidity of the 
swamps and jungles of the Devonian age, the development of living things 
took a gigantic step forward when backboned creatures first emerged from 
the sea to spend intervals on land. Some of them were enormously large, 
reptile-like, and covered with formidable armor; others were more like cer¬ 
tain fishes known from fossils of that age. Their special characteristics, 
however, were vocal expression and the ability to live on land as well 
as in the water. 
Present-day amphibians, or batrachians as they are sometimes called, 
retain these fundamental traits. However, the modern descendants of the 
most primitive of four-footed animals are much smaller, weaker and numer¬ 
ically inferior. Yet in the course of their evolution from the earliest land 
pioneers they have become more highly specialized and structurally quite 
unlike their Devonian ancestors. 
Amphibians comprise a class of vertebrates whose place in the evolu¬ 
tionary scale is between the fishes and the reptiles. Like some reptiles, 
many amphibians are able to shed their skins. A few, when full grown, 
retain their tails and even look like reptiles. 
The life history of modern amphibians parallels the slow evolution 
of their ancestors. They are born, like most fishes, from eggs generally laid 
in the water. In many species the eggs, surrounded by a gelatinous envelope 
for protection, develop into larvae or tadpoles which breathe through 
gills and propel themselves by means of their tails. At this stage they are 
limbless. 
Then a miracle of nature takes place as the creatures prepare to bridge 
the gulf separating the denizens of the water from those on land. In certain 
species the external gills are greatly reduced, the tail fin is absorbed into 
the body, the larval skin is shed, lungs form, legs begin to “sprout,” and 
eyelids are grown. Recent discoveries indicate that these changes are to 
a great extent controlled by the action of glandular secretions in which the 
thyroid plays a part. 
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