GENERAL ZOOLOGY 





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Fig. 15.42. Class Arachnida. 

 .4, a tarantula. B, a scorpion, 

 Uroctonus mordax, which has cap- 

 tured a Jerusalem cricket, Steno- 

 pelmatus lonotspina. Note the use 

 of the powerful chelate pedipalps 

 in grasping the insect, which has 

 been stung by the poison claw at 

 the tip of the scorpion's tail. {A, 

 photograph courtesy General 

 Biological Supply House, Inc.; 

 /?, photograph by E. S. Ross.) 



circulates (Fig. 15.41). The individual "pages" of the book lung contain 

 air spaces, and the collective air spaces of each lung communicate with the 

 outside through a slit-like spiracular opening. Some spiders possess, in 

 addition to or in place of book lungs, tracheal systems analogous to those of 

 insects, with segmentally arranged spiracles 



Relatively few spiders, among them the "black widow," Latrodecles mactans, 

 are dangerous to man. By far the majority of spiders are beneficial 

 through their destruction of insects (Fig. 15.42). Of even greater economic 

 importance are the arachnids called ticks and mites, many of which are 

 parasitic on man and his domestic animals, and a few of which transmit 

 disease-producing microorganisms from host to host. 



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