1 84 



SYSTEMATIC ZOOLOGY 



securely on each radial thread and continues it to the center, 

 biting away the first spiral as it advances. 



One of the largest spiders is the tarantula, common in the 

 tropics and in some of our Western states ; with legs expanded 

 it is sometimes fifteen centimeters in diameter ; it is brownish in 

 color, covered with hairs, and with its very long legs is a most 

 repulsive-looking animal. The bird spider of tropical South 

 America is another huge hairy spider, which sometimes attacks 

 and kills small birds and mice. In all spiders the female is 

 generally much larger and stronger than the 

 male, while the latter is generally marked with 

 much brighter colors than his mate. The two 

 sexes do not generally live happily together, as 

 the males are in constant danger of being killed 

 by the females ; sometimes they are found in 

 the same web, sometimes on adjacent webs, 

 but generally farther apart. Nearly all the 

 spiders are land animals, but some live a good 

 part of the time in fresh water ; there they 

 breathe by means of bubbles of air which 

 adhere to the sur- 

 face of the body 

 when they go 

 under water. 



FlG. 179. Demodex 

 follicular um , a mite 

 parasitic m hair 

 follicles ; greatly 

 enlarged. Kt, pedi- 

 palps. (After Me- 

 guin from Claus 

 and Sedgwick's 

 Text-book.) 



Order 7. Acarina 



The Acarina 

 (L a t. a c a r it s, 

 mite), the ticks 

 and mites, are 

 minute A r a c h- 



nida living on organic matter on 

 land, or in fresh or salt water, or 

 as parasites on plants or animals. 

 There is no evidence of segmen- 

 tation in the body, — head, thorax, 

 and abdomen being fused into one mass. There are six pairs of 

 appendages, — two pairs are mouth parts, and four pairs are legs ; 



Fig. i So. Sarcoptes tcaiiai, the itch mite. 

 (After Leuckart, from Parker and Has- 

 well's Manual.) 







