The Story of Evolution 93 



interesting "living fossils," binding the class of fishes to that of 

 amphibians. It is highly probable that the first invasion of the 

 dry land should be put to the credit of some adventurous worms, 

 but the second great invasion was certainly due to air-breathing 

 Arthropods, like the pioneer scorpion we mentioned. 



The Devonian period, including that of the Old Red Sand- 

 stone, was one of the most significant periods in the earth's his- 

 tory. For it was the time of the establishment of flowering plants 

 upon the earth and of terrestrial backboned animals. One would 

 like to have been the discoverer of the Devonian footprint of 

 TJiinopus, the first known Amphibian foot-print an eloquent 

 vestige of the third great invasion of the dry land. It was prob- 

 ably from a stock of Devonian lung-fishes that the first Amphib- 

 ians sprang, but it was not till the next period that they came 

 to their own. While they were still feeling their way, there was 

 a remarkable exuberance of shark-like and heavily armoured 

 fishes in the Devonian seas. 



EVOLUTION OF LAND ANIMALS 



1 



Giant Amphibians and Coal-measures 



The Carboniferous period was marked by a mild moist 

 climate and a luxuriant vegetation in the swampy low grounds. 

 It was a much less strenuous time than the Devonian period ; it 

 was like a very long summer. There were no trees of the type 

 we see now, but there were forests of club-mosses and horsetails 

 which grew to a gigantic size compared with their pigmy repre- 

 sentatives of to-day. In these forests the jointed-footed invaders 

 of the dry land ran riot in the form of centipedes, spiders, scor- 

 pions, and insects, and on these the primeval Amphibians fed. 

 The appearance of insects made possible a new linkage of far- 

 reaching importance, namely, the cross-fertilisation of flowering 

 plants by their insect visitors, and from this time onwards it may 

 be said that flowers and their visitors have evolved hand in hand. 



