THE PROGRESS OF LIFE 61 



The remains of the Brachiopods and Trilobites are 

 found chiefly in shallow-water deposits ; but some of 

 them may have pushed their way into the deep sea, 

 feeding on the dead pelagic organisms which rained 

 down from above ; indeed, it has been thought that 

 the eyeless condition of some of the early Trilobites 

 is a proof of this. But the eyes are always placed 

 on the second segment, called the free cheek ; and in 

 several of the earlier forms this free cheek is ventral 

 only, in which case no eyes could appear on the dorsal 

 surface ; the absence of eyes is not, therefore, always 

 a proof of degeneration, but there are some species of 

 Illcenus in which the eyes have disappeared. 



The hard spines of the early Trilobites could not 

 have been for defence, for there were no enemies 

 capable of attacking them ; but, perhaps, they were 

 used indirectly in locomotion. As their weak little 

 legs paddled backwards and forwards in the mud, the 

 spines, all of which are directed backwards, would 

 necessitate motion in a forward direction only. 



There is no evidence of the existence of any 

 animals sufficiently protected to live among the 

 breakers round the shore, nor is there any evidence 

 of life on the land. If a human spectator could have 

 stood on the shore at that time he would probably 

 have seen no animal life at all. The rocks below low- 

 water mark would be covered with delicate red and 

 brown seaweeds, and the ocean between tide-marks 

 would, then as now, be girdled with a belt of vivid 

 green ; but all the land above would be brown and 

 barren, without even a moss or lichen growing on it. 

 Upon the sands at his feet might lie a dead jelly-fish 

 or Trilobite, or, perhaps, a delicate transparent shell 



