22 
THE STUDY OF INSECTS . 
only one, two, or three pairs; and certain cave spiders 
are blind. Spiders breathe by means of lung-sacs, of which 
there are one or two pairs; and some have tracheae also. 
The lung-sacs open on the lower side of the abdomen 
near its base, and between them is the opening of the 
reproductive organs. The tracheae open through a single 
spiracle near the hind end of the body, just in front of the 
spinning organs. 
The spinning organs, which are situated near the end of 
the abdomen, consist of two or three pairs of spinnerets. 
These appendages (Fig. 18) are more 
or less finger-like in form, and some¬ 
times jointed. Upon the end of each 
spinneret there are many small tubes, 
the spinning tubes, from which the silk 
is spun (Fig. 19). Some spiders have 
as many as one hundred and fifty or 
two hundred of these spinning-tubes 
on each spinneret. The silk is in a 
fluid state while it is within the body, but it hardens as 
soon as it comes in contact with the air. 
In addition to the many small spinning tubes, there are 
a few larger ones, termed spigots. The ordinary thread is 
spun from two or four of these. The small spinning 
tubes are used in making attachment disks for fast¬ 
ening threads in place, in making a swathing band 
for enveloping prey, and, sometimes, in making a fig. x 9 . 
broad, wavy band across the center of a web. We *$£££* 
have observed a spider seize a large grasshopper greatly 
which was entangled in its web, and, rolling it over cnlar ^ ed * 
two or three times, completely envelop it in a sheet of silk 
spun from its spread-apart spinnerets. 
In the construction of their web some spiders make 
use of two kinds of silk. One of these is dry and inelastic ; 
the other, viscid and elastic. This fact can be easily seen 
by examining an orb-web. If the spiral line which forms 
Fig. t8. —End of abdomen of 
spider, showing six spinner¬ 
ets spread apart: in front of 
these is the spiracle, and be¬ 
hind them the open.ngot the 
alimentary canal. 
