THE LIFE OF THE SEA-SHORE. 143 
each instantly disappears, ejecting a forcible jet of water 
as it does so. If by means of hammer and chisel you follow 
the stars into the rock, you find that they are siphons or 
breathing tubes of a little white-shelled bivalve, called 
Saxicava, on account of its rock-boring habit. High up on 
the shore you may often find dry stones riddled with the 
burrows of Saxicava, with the dead shells still sticking in 
them. Such stones are often carried away as ornaments to 
rockeries. Notice that Saxicava remains permanently with- 
in its burrow. When the stones are covered by the water 
it protrudes its red tubes, and through them both breathes 
and feeds. When the tide ebbs or enemies threaten, it with- 
draws the tubes and is safe. Not a few shore molluscs 
are rock-borers, passing all their lives within tunnels of 
their own making. 
Far more numerous, however, are the burrowers in sand, 
which, if it does not form so secure a resting-place as the 
solid rock, is one more easily obtained, and is taken ad- 
vantage of by many animals. Some of you may object to 
the word ‘many,’ for you may have watched children digging 
for hour after hour, and noticed how rarely they come upon 
a living creature. But the explanation is simple enough. 
Animals which live in sand usually live on sand, and can 
therefore only flourish in sand which contains abundant 
organic particles. These are often conspicuously absent 
from the long clean stretches of beach most favoured by 
children, which are thus unsuited for the support of animal 
life. Slightly muddy sand near low-tide mark will often 
yield an abundant harvest to a patient digger. Some 
common sand burrowers may be mentioned as examples. 
Most abundant are, of course, the worms—the fishermen lob- 
worm (Arenicola), the rag-worms (Werine), and many others. 
Then near low-tide mark one may find the interesting 
heart-urchins (Zehinocardium), the spines with a beautiful 
golden tint quite absent in specimens found dead and dried 
on the beach. Many molluscs also occur, such as cockles 
(Cardium), otter shells (Zutraria), old maid sheils (Mya), all 
to be found in the living active condition. Among the 
rarer finds are burrowing sea-anemones (Peachia), and that 
curious worm-like Holothurian, known as Synapta. These 
