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know so well, minute living blobs of jelly. 'Inspired guesses' 

 based on faint signs in ancient rocks put the first appearance of 

 living matter on the earth at about 1,700 million years ago. These 

 first forms of life developed slowly and gave rise to other types, 

 some more advanced, and by 450 million years ago there were 

 numbers of 'invertebrates', backboneless creatures of many types, 

 some quite large, in most of the waters all over the earth. 



The first true vertebrates, or backboned animals, are estimated 

 to have appeared by 400-350 million years ago. They must 

 have developed from some ancestor without a true backbone, and 

 they certainly were peculiar creatures, for they had no scales and 

 notruejaws, just soft, sucking mouths. It is in one sense incorrect 

 to speak of some at least as 'backboned', for they had no true bone 

 but vertebral columns only of gristle. Some of them, however, 

 had bodies covered with heavy bony armour, and these have left 

 excellent fossil records. 



There is evidence that at the close of the Silurian period and 

 over the beginning of the Devonian some striking change was at 

 work, for it was then that fishes something like the modern types 

 we know first appeared. They had true bony jaws and overlap- 

 ping scales, and a skeleton at least partly bony. Their fins were 

 peculiar, rather like small paddles with a fringe of soft rays, so 

 that they were named 'Crossopterygii' or 'fringe finned'. 



These fishes represented a tremendous step forward in evolu- 

 tion in more ways than one. Not only did they at that very early 

 stage show important features that have remained predominant 

 in fish life to this day, but one group of them gave rise to forms 

 that colonised the land and were indeed our own ancestors. 



It would be as well to realise that up to the Devonian period 

 the land was very diff'erent from that of today. There was abundant 

 animal and plant life in the water, but apparently hardly any on 

 land, which was bare, mainly rock. Indeed, only about this time 

 did plants start to creep ashore, so that up to then there had been 

 nothing to tempt creatures to leave the water. It is strange to 

 think of static life like plants being able to move out and colonise 

 a different medium, to come out of water and march across the 

 land, but it was done. And as such things go, plants can move 

 quite rapidly in that way. If you look at a pine forest you will see 

 how trees can march across country, for there will be younger 



