The External Anatomy of Spiders 



A more complicated form of epigynum is found, for example 

 in spiders of the genus Aranea, where there is developed an ap- 

 pendage which is usually soft and flexible, and which is termed 

 the scape or ovipositor, as it is believed to have a function analogous 

 to that of the ovipositor of insects (Fig. 133). In some cases, 

 however, the form of the scape is such that it is difficult to see 

 how it can function as an ovipositor; and it may be that in these 

 cases it functions during copulation instead of during oviposition. 

 The scape of Aranea gemma (Fig. 134) will serve to illustrate this 

 point. Here the scape is immovable and the spoon-shaped tip 

 seems fitted to receive some part of the palpus of the male rather 

 than to be of use in placing the eggs. When there is a well- 

 developed scape the tip of it is usually more or less spoon-shaped, 

 this part of the scape is termed the cochlear. The basal plate of 

 the epigynum which bears the scape, and which forms a vaulted, 

 porch or hood that covers the opening of the oviduct was named 

 by McCook ('8c)-'93) the atriolum (a-tri'o-lum). 



A still more complicated form of epigynum is found in some 

 of the Linyphiidae and Argiopidae, where the ovipositor consists 

 of two finger-like projections: first, the more common one, the 

 scape, which arises from the atriolum, and consequently in front 

 of the openings of the oviduct; and second, one which arises 

 behind the opening of the oviduct; this is termed the parmula 

 (par'mu-la). Each of these projections may be grooved on the 

 face next its fellow, the two grooves forming a tube (Fig. 135). 



The entrance to the reproductive organs of the female is 

 termed the vulva; it is an open space covered by the epigynum. 

 Some writers apply the term vulva to the epigynum. 



In some spiders there is a well-defined sclerite on each side 

 of the epigynum; these sclerites are termed the lateral scleritcs. 



The epigastric plates. — There is on each side in front of the 

 lung-slit a hard plate; these are termed the epigastric plates. 



The Spinning Organs. — The spinning organs are situated 

 near the caudal end of the abdomen, on the ventral aspect, and 

 consist usually of three pairs of spinnerets, to which is added in 

 certain spiders another organ, the cribellum. 



The spinnerets. — The spinnerets are finger-like in form and 

 usually six in number (Fig. 136), although sometimes there are 

 only four, and the number may be reduced to a single pair. 



The pairs of spinnerets are usually designated as the upper, 



132 



