SPIDERS AND THEIR WEB-MAKING 



207 



mostly young, and hence small individuals of various 

 species; but some adult spiders of small size are also 

 aeronauts. 



Life-history of spiders. — The eggs of spiders are 

 inclosed in silken cases, or cocoons of various shapes. 

 Most common are the flattened circular or elongate kinds 

 attached to the under side of boards or stones. Some- 



FiG. 168. Fig. 169. 



Fig. 168. — Webs of young orb-web spiders on a large web of an old spider. 



(After McCook.) 

 Fig. 169. — Assembly of young spiders just after issuance from cocoon, 



" balled" underneath a rose-leaf. (After McCook.) 



times they are spherical or vase-shaped and are suspended 

 among the leaves. As already noted the females of 

 certain running spiders carry the egg-sac about attached 

 to the spinnerets. 



The eggs hatch in from fifteen to thirty days in sum- 

 mer, but if laid in the fall may not hatch until the follow- 

 ing spring. The young rarely leave the egg-sac imme- 

 diately but remain in it for a period ranging from a few 

 days to several weeks. With some species the spider- 



