148 THE BIDDLE OF THE UNIVEKSE. 



represent the protective arrangements which were 

 acquired by the earliest reptiles (proreptilia) , the 

 common parents of all the amniotes, in the Permian 

 period (towards the end of the palaeozoic age), when 

 these higher vertebrates accustomed themselves to 

 live on land and breathe the atmosphere. Their 

 ancestors, the amphibia of the Carboniferous period, 

 still lived and breathed in the water, like their earlier 

 predecessors, the fishes. 



In the case of these older and lower vertebrates that 

 lived in the water, the embryonic development had 

 the palingenetic character in a still higher degree, as 

 is the case in most of the fishes and amphibia of the 

 present day. The familiar tadpole and the larva of 

 the salamander or the frog still preserve the structure 

 of their fish-ancestors in the first part of their life in 

 the water ; they resemble them, likewise, in their 

 habits of life, in breathing by gills, in the action of 

 their sense-organs, and in other psychic organs. 

 Then, when the interesting metamorphosis of the 

 swimming tadpole takes place, and when it adapts 

 itself to a land-life, the fish-like body changes into 

 that of a four-footed, crawling amphibium ; instead of 

 the gill breathing in the water comes an exclusive 

 breathing of the atmosphere by means of lungs, and, 

 with the changed habits of life, even the psychic 

 apparatus, the nervous system, and the sense-organs 

 reach a higher degree of construction. If we could 

 completely follow the psychogeny of the tadpole from 

 beginning to end, we should be able to apply the 

 biogenetic law in many ways to its psychic evolution. 

 For it developes in direct communication with the 

 changing conditions of the outer world, and so must 

 quickly adapt its sensation and movement to these. 



