TRAP DOOR SPIDERS. 



363 



holss in the ground, and sometimes conceals the opening by 

 covering it with a few dead leaves. Our largest spider is 

 Nephila plumipes of the Southern States. The common 

 garden spider is Epeira vulgaris Hentz. It lives about 



c 



Fig. 320. Development of the Spider. A, worm-like stage ; B, primitive band ; 

 C, the same more advanced, with rudiments of limbs. 



houses and in gardens ; its geometrical web is very regular. 

 The large trap-door spider (Mygale) has four lung-sacs in- 

 stead of two, as in the other spiders, and only two pairs of 

 spinnerets. Mygale Henzii Girard 

 inhabits the Western plains and 

 Utah ; Mygale avicularia Linn, of 

 South America is known to seize 

 small birds, and suck their blood. 

 There are probably about six or 

 eight hundred species of spiders 

 in North America ; their colors 

 are often brilliant, and sometimes, 

 from the harmony in their colora- 

 tion with that of the flowers in 

 which they hide, or the leaves on 

 which they may rest, elude the 

 grasp of insectivorous birds. 



Sub-class 4. Hexapoda. The 

 triregional division of the body is better marked in the 

 genuine winged insects than in the Myriopods and spiders. 

 They have compound as well as simple eyes ; two pairs of 



Fig. 321. Embryo Spider, still 

 more advanced. This and Fig. SiO 

 after Claparede. 



