STAR-FISH AND SEA-URCHINS. 279 
available can be at once appreciated on witnessing 
the performance, so that one is surprised, notwith- 
standing the co-ordination displayed by all the 
suckers, that they are able to accomplish the work 
assioned to them. That the process is in truth a 
very laborious one is manifest, not only from the 
extreme slowness with which it takes place, but 
also because, as already observed, in the case of not 
perfectly strong specimens complete failure may 
attend the efforts to reach the position of resting on 
the equator—the Echinus, after rearing up a certain 
height, becoming exhausted and again falling back 
upon its ab-oral pole. Moreover, in some cases it 
is interesting to observe that when the equator 
position has been reached with difficulty, the 
Echinus, as it were, gives itself a breathing space 
before beginning the movement of descent—drawing 
in all its pedicels save those which hold it securely 
in the position to which it has attained, and 
remaining in a state of absolute quiescence for a 
prolonged time. It then suddenly begins to protrude 
all its feet again, and to continue its manceuvre. 
At any time during such a period of rest, a stimulus 
of any kind will immediately determine a recom- 
mencement of the manceuvre. 
It will be perceived that as soon as the position 
just described has been attained, gravity, which had 
hitherto been acting in opposition to the righting 
movement, now begins to favour that movement. 
It might, therefore, be anticipated that the Echinus 
would now simply let go all its attachments and 
allow itself to roll over into its natural position 
