SPIDERS AND MYRIAPODS 



239 



U. S. Bureau of Entomology 

 Is a spider an insect ? Why ? 



lunglike sacs in the abdomen. 

 They have no wings or com- 

 pound eyes. The silk with 

 which they spin their webs is 

 secreted by means of glands in 

 a liquid form. On exposure to 

 air this fluid hardens and forms 

 a very tough thread which is 

 light and strong. 



We are all familiar with the 

 harmless " thousand leggers " 

 found under stones and logs. It- 

 is a representative of the group 

 of animals known as the mille- 

 pedes. These animals have a 



rounded body divided into two regions, 

 head and trunk, and have two pairs of 

 legs on each body segment. They live 

 in damp places and feed on decaying 

 vegetable matter. They are entirely 

 harmless. The centipedes are long 

 flattened animals with one pair of legs 

 on each segment. Both the millepedes 

 and centipedes are representatives of 

 the class Myriapoda. 



Practical Exercise 8. Make four diagrams 

 to show the likenesses and differences between a 

 crustacean, an insect, a myriapod, and a spider. 

 Use books of reference for information. Use 

 colors for different structures, as yellow for exo- 

 skeletons, blue for nervous system, red for blood 

 vessel or heart, etc. 



Practical Exercise 9. Name all the arthro- 

 pods you have found living in your environ- 

 ment. Which live in water? On land? In 

 both habitats? 



Practical Exercise 10. Study the diagrams 

 of the Arthropods. How many legs has the crab, 

 the centipede, the insect, the spider? Study a 

 real crab and centipede to see how they differ 

 u. s. Bureau of Entomology from the insects. From the above study can you 

 Why is a centipede an Arthropod ? make a working definition of an Arthropod ? 



