240 FIELD ZOOLOGY. 



among the plates the air is kept in constant motion, and 

 in the spaces between them the interchange of oxygen 

 for carbonic acid gas takes place. The heart has 

 branches along the sides through which the blood is 

 sucked in, and finally the blood passes through these 

 sack-like lungs. The tracheary system also has its sepa- 

 rate openings, two of them farther back on the abdomen, 

 near the anal end. 



Unlike the insects, most spiders do not swallow their 

 victim, but chew- the body and suck at it until it is little 

 more than a mass of dry shreds. One may occasionally 

 find in a spider's web the body remnant of some insect 

 which has been so disposed of. Spiders are able to go 

 for long periods of time without food; this is fortunate, 

 for they must set their traps and wait for an insect foolish 

 enough to fall into them. They are not gregarious in the 

 least degree; each spider jealously guards its own food 

 traps. Of course, in so doing, it simply obeys the neces- 

 sary instinct of food-getting, and serves the law of self- 

 preservation. Even the male and the female spiders are 

 bitter enemies for most of their lives. The male of any 

 species may usually be known by the fact that he has 

 longer legs and a slenderer abdomen — a fortunate 

 provision that often saves him from being eaten by the 

 fiercer and hungry female. 



The sense of touch seems to be well developed. A 

 spider, waiting for a bite, sits patiently in its web, if it 

 is of the web-spinning sort. The wind may shake the 

 web, a twig may fall through it, and the spider pays no 

 attention. But let even a small insect hit one of the 

 gossamer threads, and the alert spider is on its victim 

 in an instant, either binding it with threads newly-spun; 

 if it is large and threatens to tear the web and .escape, or 



