2 Annals Entomological Society of America iolkaye 
creatures are in the cephalothorax and open through the tips of 
one pair of jaws, the chelicerze, while the silk glands of spiders 
are in the abdomen and open through specialized legs at the 
opposite end of the body. Any genetic connection that there 
may be between these two sets of silk organs is too remote to 
throw any light on the particular problem before us. It is 
evident that in our study of the evolution of spider webs we are 
forced to confine our attention to the habits of spiders. 
It is probable that the production of silk by spiders was not 
primarily evolved for the making of webs for capturing prey. 
The representatives of many families do not spin webs; and 
there is no reason to believe that these non-web-making families 
have descended from web-making forms. It seems more 
probable that the use of silk for making webs for capturing prey 
is a secondary or tertiary adaptation. 
All spiders use silk in caring for their eggs. And it seems 
probable that this was the primary use of silk in this group 
of animals. 
With some spiders, as Pholcus, only a little silk is used for 
this purpose, merely enough to fasten the eggs together in a 
ball; with some spiders the habit of making an elaborate egg-sac 
has been evolved; and many types of these egg-sacs exist. A 
single illustration of an elaborate egg-sac is sufficient for our 
present purpose. Glyptocranium cornigerum makes an egg-sac, 
with a vase-shaped outer covering, and fastens it to a twig 
with bands of silk in a manner which almost suggests human 
intelligence. 
Spiders having acquired silk for the protection of their eggs 
have utilized it for other purposes, of which the making of webs 
for capturing prey is but one, and probably not the next one 
in the sequence of the different uses of this substance. 
Many spiders that live in burrows in the ground strengthen 
the walls of their burrows by a lining of silk. Some of these, 
the well-known trap-door-spiders close the entrance to their 
nest by an elaborately constructed lid; and some build a turret 
over the entrance of their burrow. In the case of the turret 
spiders we have, I believe, from observations made on one that 
I kept in confinement in my office for several months, species 
that build a structure to facilitate the capturing of their prey, 
the turret serving as a watch tower from which insects invading 
the region near the nest can be more easily seen. 
