BRANCH ARTHROPODA ; CLASS ARACHNID A : SPIDERS 229 



plates. The true centipeds (Scolopcndra) (fig. 88) have 

 twenty-one to twenty-three body-rings, each with a pair 

 of legs, and the antennae have seventeen to twenty joints. 

 They live in warm regions, some growing to be very 

 large, as long as twelve inches or more. The " bite " or 

 wound made by the poison-claws is fatal to insects and 

 other small animals, their prey, and painful or even 

 dangerous to man. The popular notion that a centiped 

 " stings " with all of its feet is fallacious. It is recorded 

 by Humboldt that centipeds are eaten by some of the 

 South American Indians. 



CLASS ARACHNIDA: THE SCORPIONS, SPIDERS, MITES, 

 AND TICKS. 



TECHNICAL NOTE. Obtain specimens of various spiders ; the 

 running or hunting spiders may be found on the ground, especially 

 under stones and boards, the web-makers on their snares. Get 

 also spiders' " cocoons " (egg-sacs). Examine the external structure 

 of the spider ; note the two body-regions ; the number and character 

 of legs ; the absence of antennas ; the number and arrangement of 

 the eyes (which are simple, not compound) ; the mouth-parts, espe- 

 cially the large mandibles ; the spinnerets at the tip of the abdomen 

 (examine a cut off spinneret under the microscope to see the spin- 

 ning-tubes) ; note the breathing openings or spiracles on under side 

 of abdomen. Obtain also a scorpion if possible, and some ticks and 

 mites. Compare with the spiders and note that in the scorpion 

 the body is plainly seen (especially in the abdomen) to be composed 

 of segments. Note the extreme fusion of the segments and body- 

 regions in the mites and ticks. The common red spider of hot- 

 houses and gardens is a mite ; ticks may sometimes be found on 

 dogs. Observe various kinds of spider-webs, and try to observe 

 the process of web-making (this can be observed early in the morn- 

 ing or about dusk) by one of the orb-weaving garden-spiders. 

 Live spiders can be kept in the schoolroom and their feeding 

 habits and perhaps web-making habits observed. 



The class Arachnida is composed of Arthropods whose 

 body-segments are grouped into two regions, a cephalo- 

 thorax bearing the mouth-parts, eyes, and legs, and an 

 abdomen. The segments composing these two parts are 



