HOMES AND DOMESTIC HABITS 259 



145. Spiders. Most spiders spin silken cocoons or sacs 

 in which to deposit their eggs. Some spiders carry this 

 egg-filled cocoon about with them for the sake of protect- 

 ing the eggs. After hatching, the spiderlings remain in the 

 cocoon a short time, feeding on each other ! Thus only the 



FIG. 15G. Sea-urchins living in holes bored into rocks of the seashore below high- 

 tide line. 



strongest survive and issue from the cocoon to earn their 

 living in the outer world. With certain species of spiders 

 the young after hatching leave the cocoon and gather on 

 the back of the mother and are carried about by her for 

 some time. In connection with their webs or snares many 

 spiders have silken tunnels or tubes in which to lie hidden, 

 a sort of sheltering nest. Those spiders that live on the 

 ground make for themselves cylindrical burrows or holes 

 in the ground, usually lined with silk, in which they hide 

 when not hunting for food. Especially interesting among 

 the many kinds of these spider nests are the burrows of 

 the various trap-door spiders. These spiders are common 

 in California and some other far Western States. The bur- 



