42 THE SEA-SHORE 



means of their byssus threads. First they move 

 a few of these threads forward, and take a fresh 

 hold with them ; then they draw the rest up after 

 them ; and then they move the front ones forward 

 once more, and so on over and over again. 



Mussels are very largely used for food, and 

 also as bait for deep-sea fishing. In the Firth of 

 Forth alone, indeed, nearly forty millions of these 

 creatures are collected every year for this latter 

 purpose alone, or one for every man, woman, and 

 child in England and Scotland and Wales ! 



PLATE XIV 

 THE HORSE MUSSEL (3) 



This is not a very handsome creature, for its 

 shell is covered all over with a rather thick brown 

 skin, which is very much wrinkled. It is quite 

 common in many places, and yet one does not 

 very often see it; for it is nearly always hid- 

 den underneath its byssus threads, which grow 

 in thick masses. Besides this, it often burrows 

 underneath the surface of the sand; so that 

 unless you know just where to look for it, and 

 how to look for it, you are not likely to find it. 



But if you go down to the pools at the very 

 edge of the water when the tide is quite low, 

 and scrape away the sand which is heaped up 



