22 



EVOLUTION IN THE PAST 



Some drifted about on pieces of seaweed (Phillograptus, 

 Didymograptus) ; others having developed a disc to act as 

 a fl oa t and looking like attenuated brittle-stars had be- 

 come free of adventitious support (Dichograptus). Such 

 colonies, however, were no doubt more or less at the mercy 

 of the currents ; for it is not likely that the zooids had 

 developed a central navigating authority. The colony had 

 freedom, but was without any organised ability to regu- 

 late it. 



Graptolites attained an extraordinary development during 

 this Period. They seem to have been collected often in large 

 companies, and to have thriven best in muddy waters. 

 Widespread also was their range ; for traces of them have 

 been found in Europe, America (North and South), and 

 Australia. 



CYSTIDS The little bud -like cystids showed some progress over 

 their Cambrian ancestors. The plates of the body-covering 

 were more symmetrically arranged ; and the animals could 

 better withstand the pressure of sea-currents (Echino- 

 sph&ra, Cryptocrinus). Many of them were now provided 

 with small "arms," and enjoyed, therefore, greater facilities 

 for obtaining food. This was no small gain for animals 

 rooted to the ground, and incapable, therefore, of pursuing 

 prey. No stems, at least of any note, had as yet been de- 

 veloped ; and the round little creatures seldom bigger than 

 walnuts must have had a squat and dumpy appearance 

 beside their near relations, the " sea-lilies." 



SEA-LILIES Crinoids, or " sea-lilies " scarce in the Cambrian were 

 variously developed, and easily first among the beauties 

 of the sea. Some, indeed, had their " arms " bare 

 and feebly developed, but they were by no means devoid 

 of grace. The arms of many, however, were long, finely 

 formed, and edged with feathery out-shoots (Glyptocrinus, 

 etc.). Utility, of course, was the object, and beauty had 

 come by the way. Long arms gave good reach for food, 

 and feathery appendages were useful for sweeping the supplies 

 down to the mouth, and also for aiding respiration. A few 

 forms had undergone changes which, no doubt, greatly 

 added to their enjoyment of life (Ichthyocrinidce). With all 



