370 



PHYLUM ARTHROPODA. 



stigmata of the lung-books lie on the anterior ventral surface 

 of the abdomen ; the tracheae 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 spinnerets 

 are transformed abdominal appendages (a new organ from 

 an old as is so often the case); and the glands are 



ectodermic invaginations. 

 d. 



Many spiders have at the 

 base of their spinnerets a 

 transverse surface or cribrel- 

 lum 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 

 smaller and often more 

 brightly coloured than their 

 mates. From the paired 

 testes, in the anterior part 

 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 



FIG. 194 Section of lung-book. 

 After Macleod. 



d. % Dorsal ; v., ventral ; /., lamellae ; /., 

 posterior; a., anterior; d.c,, dorsal 

 chamber; jr., posterior wall; st. t 

 stigma ; cA., one of the interlamellar 

 chambers. 



