l8S THE SPIDERS OF EPPING FOREST'. 



species, three pairs, however, being usually present. 

 The spinners are more or le^s cylindrical, conical or 

 mammiform and each is furnished with numerous small 

 Spinning Tubes, each of which is capable of emitting a 

 single silken thread. In some species an extra or super- 

 numerary spinner, termed a Cnbellum, is present. This 

 organ is of a type different from the normal spinners, in 

 front of which it is placed. Its form is very constant 

 in the various families in which it occurs, being a trans- 

 verse strip often with a central constriction, this latter 

 indicating, apparently, that it has been formed by the 

 fusion of a pair of abdominal appendages. 



Spiracular organs. Two forms of respiratory organs are 

 found in the Araneae — Luminal Tracheae and Tiibe 

 Tracheae. The laminal tracheae, sometimes termed 

 sac-tracheae, lungs, lung-sacs, or lung-books, are 

 situated beneath the integument of the inferior surface 

 of the abdomen. The organs themselves each consist 

 of a number of exceedingly delicate laminae plentifully 

 supplied with very minute vessels and communicating 

 by a narrow transverse aperture with the atmosphere. 

 The integument covering each laminal trachea is often 

 of a different tint from the surrounding portions, and 

 these parts are termed the Spiraculav-plates. The tube 

 tracheae open sometimes in one aperture and sometimes 

 in two apertures, usually close to the spinners, but 

 occasionally upon other parts of the under surface of the 

 abdomen. 



Reproductive organs. The sexual secretory glands of the 

 male and the entire reproductive system of the female 

 are situated within the abdomen, their external openings 

 being placed with few exceptions, between those of the 

 laminal tracheae. In the male the opening is very 

 minute and inconspicuous, but in the female it is often 

 provided with variously formed Epigynal Plates. In 

 some cases the integument upon the anterior side of the 

 female genital aperture is chitinised, produced down- 

 wards and backwards, and more or less modified in 

 form, the resulting structure being known as the Clavns. 

 The genital armature of the female is usually a most 

 important criterion in the differentiation of obscure and 

 closely allied species. 



