370 PHYLUM ARTHROPODA. 
stigmata of the lung-books lie on the anterior ventral surface 
of the abdomen; the trachez open posteriorly near the 
spinnerets, or just behind the opening of the lung-books, or 
at both places. 
The spinnerets (4-6) lie just in front of the anus. They 
are movable and perforated by numerous (often many 
hundred) tubes or “spinning spools,” each of which is 
connected with a compressible gland secreting silk. There 
are various kinds of glands; both the amount and the 
nature of the secretion are under control. The spinnercts 
are transformed abdominal appendages (a new organ from 
an old—as is so often the case); and the glands are 
ectodermic invaginations. 
Many spiders have at the 
base of their spinnerets. a 
transverse surface or cribrel- 
um perforated by spinning 
tubes, and from this they 
comb out a peculiar curled 
silk with the help of a row 
of stiff bristles or calamistrum 
on each posterior leg. 
The males are usually 
Fic. 194 —Section of lung-book. smaller and often more 
“Hitter Map IRou brightly coloured than their 
d., Dorsal; v., ventral; 2., lamella; ., mates. From the paired 
posterior; @., anterior; d.c., dorsal 7 , 
chamber; x., posterior wall; s¢., testes, in the anterior part 
stemes fg one of the interlamellar of the abdomen, two vasa 
deferentia pass to a com- 
mon aperture beside the openings of the lung-books. 
From the paired ovary two oviducts likewise arise and open 
into a uterus, whose external aperture is surrounded in the 
mature female by a complex genital armature or epigynium. 
Here also in most females are the openings of two recep- 
tacula seminis, in which the sperms received from a male are 
stored, and from which they pass by a pair of internal ducts 
to the oviducts, there to fertilise the ova. The sperms of 
the male, after emission, may be stored up in the last joint 
of the palps. The ova are usually surrounded by silken 
cocoons, which are carried about by the mother or carefully 
hidden in nooks or nests. There is no metamorphosis ‘but 
