410 ZOOLOGY 
are four conical two-jointed spinnerets, whose apices meet 
together when at rest; if these be separated, two smaller 
single-jointed spinnerets are disclosed. Each of these projec- 
tions is very mobile, and they can be separated and approximated 
with ease. They are perforated at their apices by a number 
of minute pores, amounting to about 600 in all, through which 
the “silk” leaves the body. This silk is secreted by an enor- 
mous number of glands which lie in the abdomen ; these in the 
species in question are of five distinct kinds. Each kind of 
gland has not only a definite relation to the spinnerets, some 
supplying two pairs and others only one, but the threads 
secreted from the various kinds of glands differ in quality, and 
are used for different purposes. Thus the lines in the con- 
centric threads of the well-known wheel-like webs differ from 
the radial lines in being sticky, and so serving to hold the 
captured flies, etc., and these again differ from the threads 
which form the cocoon, or from those used to bind up captured 
prey; and each of these various kinds of thread is the product 
of one definite set of glands. 
Between and a little behind the posterior spinnerets the 
anus is situated. 
In Lpeira the two stigmata leading to the pulmonary sacs 
are on a level with the genital orifice. The cavities of the two 
pulmonary chambers are in communication with one another 
across the median line. Lach cavity is to a great extent 
occluded by a number (about sixty) of horizontally placed 
lamellae, which are attached as a rule to the wall of their 
sac by their anterior and lateral edges, but present a free 
edge posteriorly. These lamellae have very thin chitinous 
walls, which are prevented from collapsing by the presence of 
a number of little cellular pillars. Between the dorsal and 
ventral wall of each lamella the blood circulates, whilst the 
air passes in the slit-like spaces between the neighbouring 
lamellae. 
In addition to the pulmonary sacs, Hpeiva also has a 
tracheal system. A single stigma opens just in front of the 
anterior spinnerets, and leads into a median sac; from this 
four tracheae emerge. These are chiefly distributed to those 
organs which lie behind the pulmonary sacs. In other species, 
