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 Hchi- 
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 Linnzeus 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 “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 
