HABITS OF MARINE ANIMALS 141 
star-fish thus becomes the rounded urchin, and the 
under-surface of the five fingers of the former, are now 
on the outside of the latter, and thus the tube-feet in 
the urchin are arranged along five radii from the base 
to the apex of this dome-shaped echinoderm. 
With its tube-feet the urchin attaches itself to rocks, 
stones and weeds, and uses them also as a means of 
progression. When used for the latter purpose, the 
tubes are extended and attached to the rocks by means 
of the suckers, and then by their contraction the urchin 
pulls himself up to the points of attachment. 
These tube-feet are only visible when extended, 
but the numerous spines on the outer cover of the urchin 
are apparent at all times, and each has a cup-shaped 
base which works on a knob on the outer cover, thus 
giving the spines a considerable range of movement. 
Though mainly provided for protective purposes, the 
urchin uses these spines as an adjunct to the tube-feet, 
in order to steady himself as he climbs or moves about. 
When in a hurry, however, he is able to scuttle along 
level ground on his spines alone, without using his 
tube-feet. The mouth is in the centre of the under- 
surface, and is furnished with five sharp cutting teeth, 
which are easily seen. Among the other functions of 
the tube-feet is that of carrying food to the mouth. 
It was low tide as we climbed along the old break- 
water, and numerous urchins, the size of large oranges, 
were high and dry, attached to the concrete blocks. 
The photograph of one taken in this position shows 
