226 THE SCIENCE OF LIFE. 



of palpiform organs. The mandibles are vertical, and 

 end in a powerful hook. The maxillae, or palpi, which in 

 Scorpions are powerful claws, in Spiders resemble thor 

 racic feet. The brain is of large size, and the nervous 

 system greatly concentrated. 



The instincts of Spiders are very remarkable. They 

 are the most wily of Articulates. They display great 

 skill and industry in weaving their webs, and some spe- 

 cies (called Mason-spiders) excavate cavities in the 

 ground, which they line with a silken web, and close the 

 entrance with a lid which moves upon a hinge. 



5. MYRIAPODA (myrios, numerous ; pous, foot) is a 

 small class, including the Centipedes and the Millipedes. 

 The body is divided into segments, twenty or more, 

 to each of which legs are appended. They resemble 

 Worms in their form, and in the simplicity of their nerv- 

 ous and circulatory systems; but the skin is hardened 

 by chitine and the legs are articulate. They breathe 

 by trachea, or tubes, have two antennae, and a variable 

 number of eyes. 



I.) Chilognatha, (cheilos, lip; gnathos, jaw.) This or- 

 der contains the Thousand -legged Worm, (Julus.') 

 The body is round, legs very numerous, sometimes a 

 hundred pairs, each segment having two pairs. Mouth 

 without palpi. Lower lip composed of confluent max- 

 illae. They are of slow locomotion, harmless, and vege- 

 tarian. 



2.) Chilopoda, (cheilos, lip ; pous, foot,) are characterized 

 by a flat body, with fifteen to twenty pairs of legs. The 

 mouth possesses a hollow duct for the passage of fluid 

 from a poison-gland. The terminal section of the body 



