8 WILLIAM PATTEN. 



the chelicerae snap and work alternately back and forth^ as 

 though tucking something into the mouth ; at the same time 

 the metastoma are moved forward and backward. But the 

 most constant feature is the following movement of the 

 second to the fifth pair of appendages; the second and 

 fourth pairs of mandibles move in unison inward toward the 

 median plane, and downward toward the mouth; then back 

 again in the reverse order. When they are farthest from the 

 mouth the corresponding legs (except the second pair in both 

 males and females) are quickly raised, flexed, and the tips 

 carried toward the mouth, where they remain an instant, and 

 then fall back on to the under side of the carapace ; the corre- 

 sponding jaw movement then begins again. The third and fifth 

 pairs of appendages and the corresponding jaws work in unison 

 in the same manner, but they alternate with those of the second 

 and fourth. At intervals these movements cease, the abdomen 

 is raised, and the stout crushing mandibles on the sixth pair 

 of appendages, which have heretofore remained motionless, are 

 slowly closed with great force, as though to crush some object 

 too large to be swallowed whole, or to kill some struggling 

 prey. These powerful jaws then slowly relax their convulsive 

 grasp, and the chewing movements are resumed. All these 

 movements go on with the greatest precision and regularity, 

 so that any food placed on the jaws is forced into the mouth, 

 and gradually disappears down the oesophagus. These chew- 

 ing movements are produced when drops of soluble food, or 

 almost any bit of animal matter, or wads of blotting-paper wet 

 in nutritive animal fluids, come in contact with the mandibles. 

 Drops of water from the interior of a clam will set the whole 

 complicated mechanism to working in exactly the same manner 

 as during the actual process of eating. Again, chewing move- 

 ments of the mandibles are produced whenever ammonia 

 vapour, ether, or chloroform is blown over them with a medicine- 

 dropper, or when they are stimulated by a weak interrupted 

 current ; but in such cases these movements are rarely accom- 

 panied by the leg movement. If the irritation with ammonia or 

 acids has been rather great the mandibles work apparently as 



