ANNALS 
Oke: 
The Entomological Society of America 
Volume V NWeACR Grea 191 2 Number 1 
THE EVOLUTION OF THE WEBS OF SPIDERS. 
By J. H. Comstock, Cornell University. 
ABSTRACT. = 
- The making of its wonderfully regular web by an orb-weaving 
spider is a remarkable instance of specialization in habits; and 
correlated with this are equally remarkable specializations of 
structure. In the construction of their webs some spiders use 
several distinct kinds of silk, to produce which several distinct 
sets of silk glands have been evolved; and to manipulate this. 
silk elaborate spinning organs have been developed. 
The tracing of the steps by which these specializations have: 
been evolved must be, in the present state of our knowledge,. 
largely conjectural. We are forced to follow the method 
commonly employed in constructing genealogical trees. We 
will look for generalized conditions and from these attempt to 
trace the evolution of those more specialized. 
A very little study by this method is sufficient to show that 
the web-making habit has not progressed in a single direct line. 
Beginning with the simplest type of web, we find that this type 
has been modified in widely different ways in the different 
families of spiders. 
In our search for a starting point we gain no help from a 
study of other arachnids than spiders. Silk organs are of rare 
occurrence in the other orders of the Arachnida. It is said that 
the tailless whip-scorpions carry their eggs in a sac formed of a 
dark brown transparent material containing some threads; but the 
source of this material has not been described. It is well-known 
that the Pseudoscorpions spin silk; but the silk glands of these 
*This address, delivered at the annual meeting in Washington, D. C., Dec. 
27, 1911, was illustrated by lantern slides made from photographs of the webs 
described. These photographs are reproduced in a volume on the Arachnida of 
North America, ‘‘ The Spider Book,’ by J. H. Comstock, now in press. 
It 
