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 climber 1 plong 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 



