142 NEW ZEALAND NATURE-STUDY BOOK 
into small flattened air-chambers, the walls of which are 
folded into a number of delicate leaf-like plates. These 
are the breathing organs of the spider. The blood circu- 
lates through these delicate folds, and is thus brought into 
contact with the air, which is drawn in and forced out by a 
special set of muscles. In addition to the air-chamber 
spiders possess tracheze through which respiration is carried 
on. 
Making the thread. At the end of the abdomen on 
the under side are little round swellings. These are the 
spinnerets with which the spider makes its silken thread. 
Hach spinneret consists of hundreds of fine tubes through 
which the animal is able to squeeze the 
liquid made by the spinning glands. 
The ends of the hind feet terminate in 
claws, which are split up along the margin 
into a number of teeth. These claws are 
known as combs and by their means the 
spider is able to twist into a single line 
the thousand of delicate threads which 
Fig. 96.—Hind foot. come from the spinnerets. The advan- 
tage of this is obvious. The lquid made 
by the spinning glands hardens on being exposed to the 
atmosphere, but the hardening process is greatly hastened 
by separating the fluid in this way and so exposing a greater 
surface to the air. The strength of the finished thread 
moreover is largely increased by twisting a number of 
strands together ; just as a wire rope is much stronger than 
an iron rod of the same thickness. 
Making the web. In making the web the spider 
stretches a strong thread between two supports. This it 
does either by fastening one end, dropping down to the 
ground, and walking across to the opposite support; or by 
letting a long thread float loosely in the air until the wind 
