24 



THE STUD Y 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 



1^ / season a large number of eggs — five hun- 



^2/ 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. 2 3 .— E^-sac of the spring those which survive emerge 

 (Frtm ' wiide'/./ 1 ' 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 Nepkila 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- 



