SURVEY OF INVERTEBRATES 



95 



Arachnoidea. We conclude the Arthropod phylum with the 

 class Arachnoidea: the Spiders, Ticks, Mites, Scorpions, and their 

 close relatives, These are frequently confused with Insects, but the 

 more common forms, such as the Spiders and Ticks, are readily 

 distinguished by the possession of eight legs. (Fig. 55.) 



Spiders are carnivorous animals that capture their prey by 



elaborately constructed webs, or by stalking and pouncing upon 



/ \ it. Some Spiders are poisonous and their repu- 



i % tation has served to malign many harmless 



relatives. But the Scorpions are in general 



Hand 



Pedipalp 

 ^Lateral eyes 

 ^•<jMedian eyes 



A B C 



Fig. 55. — A, Spider, Epeira verrucosa (from Emerton); B, Scorpion, Buthus 

 occilanus (from Krapelin); C, King-crab, Limulus polyphemus. 



poisonous, and the Mites and Ticks are injurious to Man in many 

 ways. Some bite and others burrow into our bodies and those of 

 our domestic animals; the common Rabbit frequently harbors 

 several thousand Ticks. Even our garden crops and forests suffer. 

 Unfortunately certain species infect their hosts with various Bac- 

 teria and Protozoa and so produces serious diseases. But there 

 are many harmless forms, represented by the well-known red 

 Harvest Mites. 



And then appended to the Arachnoidea is the peculiar marine 

 King-crab, or Limulus, that is of considerable theoretical interest 

 to students of evolution. (Fig. 55, C.) 



