112 BOYS AND GIRLS IN BIOLOGY. 



like chickens in a nest. Each one has his own little 

 mantle and shell, and the parts of the shell are three- 

 cornered, and at one of the corners is a little hook or 

 tooth (Fig. 105). Hanging down from the shell are a 

 whole lot of fine threads called a byssus, because they 

 look so much like fine flax, or hemp. This fine rope, or 

 byssus, is found only in the infants, they drop it when 

 they grow up ; but the salt-water mussels keep theirs all 

 their life, and use it as a cable to anchor themselves to 

 the rocks, and they can slip this anchor when they 

 please and throw out a fresh one. Soon after the little 

 ones are hatched they may be found all tangled up 

 in masses, wound about with these fine, flaxy ropes, in- 

 side the parent-shell ; but they soon untangle them- 

 selves and leave their mother's house by the little back- 

 door, or dorsal siphon, and they swim about by the 

 flapping of the three-cornered parts of the shell. This 

 looks like a very dangerous move of the mussel, be- 

 cause it is so very young to make its way in the world 

 of waters. But they are knowing little fellows of their 

 age, so, instead of " paddling their own canoe," they 

 jump on board the first boat that goes past, which hap- 

 pens to be a fish, such as a stickleback or a roach, tak- 

 ing first-class passage, for you always find them at the 

 stern, or tail, of the fish, and they keep themselves from 

 being washed overboard by hooking the little spines, or 



