MOTIONS OF ANIMALS. 105 



canal, an extremely glutinous substance is secreted, which the 

 animal, by the operation of certain muscles, has the power of 

 forcing out, and of attaching, in the form of strong threads, 

 to stones or other solid bodies. More than a hundred and 

 fifty of these cables are often employed in mooring a single 

 muscle. The substance of the threads is exceedingly viscous, 

 indigestible in the human stomach, and is probably the cause 

 of those fatal consequences which sometimes happen to inat- 

 tentive eaters. In Scotland, these threads are called the 

 beards of muscles, and should be carefully pulled off before 

 the animals are thrown into the stomach. 



Other bivalved shell-fish, the species of which are numerous, 

 perform a prog'/essive or retrograde motion, by an instrument 

 that has no small resemblance to a leg and foot. But the 

 animals can, at pleasure, make this leg assume almost every 

 kind of form, according as their exigencies may require. By 

 this leg they are not only enabled to creep, to sink into the 

 mud, or disengage themselves from it, but to perform a motion 

 which no man could suppose a shell-fish were capable of per- 

 forming. When the tellina, or limpin, is about to make a 

 spring, it puts the shell on the point or summit, as if with a 

 view to diminish friction. It then stretches out the leg as far 

 as possible, makes it embrace a portion of the shell, and by 

 a sudden movement similar to that of a spring let loose, it 

 strikes the earth with its leg, and actually leaps to a consider 

 able distance. 



The spout-fish has a bivalved shell, which resembles the 

 handle ojf a razor. This animal is incapable of progressive 

 motion, on the surface ; but it digs a hole or cell in the sand, 

 sometimes two feet in depth, in which it can ascend and de- 

 scend at pleasure. The instrument or leg by which it per- 

 forms all its movements is situated at the centre. This leg is 

 fleshy, cylindrical, ana 1 pretty long. When necessary, the 

 animal can make the termination of the leg assume the form 

 of a ball. The spout-fish, when lying on the surface of the 

 sand and about to sink into it, extends its leg from the infe- 

 rior end of the shell, and makes the extremity of it take on 

 the form of a shovel, sharp on each side, and terminating in 

 a point. With this instrument the animal cuts a hole in the 

 sand. After the hole is made, it advances the leg still farther 

 into the sand, makes it assume the form of a hook, and with 

 this hook, as a fulcrum, it obliges the shell to descend into the 

 < hole. In this manner the animal operates till the shell totally 

 disappears. When it chooses to regain the surface, it puts 



