HOMOLOGIES. 207 



The ancients knew little about them. The only 

 one to be found in the European seas resembles 

 the free Star-Fishes closely, and is now called 

 Comatula ; but even Aristotle was ignorant of its 

 true structural relations, and alludes only to its 

 motion and general appearance. Some account 

 of the gradual steps by which naturalists have 

 deciphered the true nature of these lowest Echi- 

 noderms and their history in past times may not 

 be without interest, and is very instructive as 

 showing how such problems may be solved. 



In the sixteenth century some stones were 

 found bearing the impression of a star on their 

 surface. They received the name of Trochites, 

 and gave rise to much discussion. Naturalists 

 puzzled their brains about them, called them star- 

 shaped crystals, aquatic plants, corals ; and to 

 these last Linnaeus himself, the great authority of 

 the time on all such questions, referred them. 

 Beside these stony stars, which were found in 

 great quantities when attention was once called 

 to them, impressions of a peculiar kind had been 

 observed in the rocks, resembling flowers on long 

 stems, and called a stone lilies" naturally enough, 

 for their long, graceful stems, terminating either 

 in a branching crown or a closer cup, recall the 

 lily tribe among flowers. The long stems of these 

 seeming lilies are divided transversely at regular 

 intervals ; the stem is easily broken at any of 



