272 JELLY-FISH, STAR-FISH, AND SEA-URCHINS. 
The Echinus crawls in the same way as the 
common Star-fish; but besides its long suckers it 
also uses its spines, which by their co-ordinated 
action push the animal along. The suckers, more- 
over, in being protruded from all sides of a globe 
instead of from the under side of a flat organism, 
are of much more use as feelers than they are in the 
Star-fish. Therefore, while advancing, the feet 
facing the direction of advance are always kept 
extended to their fullest leneth, in order to feel for 
any object which the animal may possibly be 
approaching. When a perpendicular surface is 
reached, the Echinus may either ascend it or not, as 
in the case of the Star-fish. While walking, the 
animal keeps pretty persistently in one direction 
of advance. If it be partly rotated by the hand, 
it does not continue in the same direction, but 
continues its own movements as before; so that, 
for instance, if it is turned half round, it will 
proceed in a direction opposite to that in which 
it had previously been going. When at rest, some 
of the feet are used as anchors, and others protruded 
as feelers. 
Regarded from the standpoint of the evolutionist, 
we have here an interesting series of gradations. 
At one end of the series we have the Echinus with 
its rays all united in a box-like rigid shell. At 
the other end of the series we have the Brittle-stars 
and Comatule with their highly muscular and 
animals, nevertheless in this particular case and in virtue 
of special modification, a Star-fish should have adopted the plan 
or mechanism of a Jelly-fish. 
