THE STUDY OF INSECTS. 



Spiders make use of silk in the construction of their 

 webs or snares, in the building of tubes or tents within 

 which they live, in the formation of egg-sacs, and in loco- 

 motion. 



Fig. 23 represents the large egg-sac of one of the orb- 

 weavers. This is made in the autumn, and contains at that 

 season a large number of eggs — -five hun- 

 dred or more. These eggs hatch early in 

 the winter ; but no spiders emerge from 

 the egg-sac until the following spring. If 

 egg-sacs of this kind be opened at differ- 

 ent times during the winter, as was done 

 by Dr. Wilder, the spiders will be found 

 to increase in size but diminish in num- 

 ber as the season advances. In fact, a 

 strange tragedy goes on within these 

 egg-sacs: the stronger spiders calmly 

 devour their weaker brothers, and in 

 Fig. 23.— Egg-sac of the Spring those which survive emerge 

 (Frim'*'wiider.r"''' sufficiently nourished to fight their bat- 

 tles in the outside world. 



The egg-sacs of the different species of spiders vary 



Fig. 24.— Egg-sac of Nephila plumipes. (From Wilder.) 



greatly in form. In some, as in that figured above, the outer 

 covering is very dense, while in others the outer part con- 



