CHEYLETUS. 287 



CASE mites, they advance by making repeated little bounds, which 

 they can execute backwards as well as forwards. They seem 

 to shun the society of their brethren, and when they meet them, 

 they give themselves up to combat, in which their chief aim is to 

 seize one another by their enormous maxillary palpi. These soli- 

 tary habits are only what one would expect from the possession 

 of such powerful offensive weapons. Whenever an animal has 

 powerful offensive weapons, it lives by rapine, and whoever 

 lives by rapine must be solitary. Any effort at making them gre- 

 garious would meet the fate of M. Le Bon's spiders. They were 

 gregarious only until they had all eaten up one another, when 

 the last survivor resumed the solitary life for which he had been 

 intended by nature. Cheyletus forms no exception to the rule. 

 Koch, when he left these animals together between two glasses, ob- 

 served them seize the cheese mites between their palpi, and plunge 

 their rostrum into their body and suck the soft parts, and Mr. 

 Beck, who has kept them in confinement, and studied their 

 habits, speaks positively to their carnivorous habits, and it would 

 almost appear that they must have something similar to the 

 poisonous powers of the spiders, and that if so a part of the 

 palpi, probably the outer and more formidable of the projecting 

 jaws, in which may be a poison gland, must be equivalent to 

 the falces of the spider. Mr. Beck says that when this Acarus 

 seizes another one of a different kind, which it does by its 

 falces laying hold of a leg or any other part indiscriminately, 

 the prey, after a lapse of about fifteen or twenty seconds, be- 

 comes poisoned or paralyzed, the legs bend up under the thorax, 

 and no part of its body makes any resistance to the pulling of the 

 devourer, who, when it finds this passive condition of the prey, 

 deliberately sucks out the fluids with an apparatus at the mouth, 

 and does not leave it until it is entirely empty and shrunken. The 

 poison does not operate, however, when tried on its own species. 

 It frequently feeds upon them, and in that case the prey continues 

 to move and show signs of life so long as any fluids appear to be 



