The External Anatomy of Spiders 



As the epigynum varies greatly in form in different species, 

 even in closely allied ones, it often affords the most distinctive 

 characteristics for recognizing species; but these features are not 

 fully developed until the spider reaches maturity. 



In its more simple form the epigynum is merely a lid-like 

 plate covering or accompanying the opening of the oviduct; it 

 is a chitinized portion of the cuticula of the segment in front of 

 the epigastric furrow; and it is situated on the middle line of the 

 body at or very near the hind margin of this segment. 



As explained in the following chapter, there are connected 

 with the internal reproductive organs of the female one or more 

 pouches for receiving and retaining the spermatozoa, the sperma- 



X 



Fig. 131. DIFFERENT TYPES OF EPIGYNA 

 a, Pirata montanus b, Trabca aurantiaca c, Lycosa pikei 



theccE. When there is a single spermatheca, as in Segestria, it 

 opens on the middle line, behind the opening of the oviduct. 

 But in most spiders there are two spermathecae which open 

 separately, one on each side of the opening of the oviduct; and 

 when there is a specialized epigynum, these openings are con- 

 nected with it. In fact it seems probable that the primary 

 function of the epigynum is to receive and direct the palpal 

 organ of the male, and that the various specific forms of epigyna 

 are correlated, in each case, with corresponding specific differ- 

 ences in the palpus of the male; these peculiarities tending to 

 prevent the union of individuals of different species. Frequently, 

 when there is a well-developed epigynum, the openings of the 

 spermathecae are on the outer face of the epigynum and can be 

 easily seen (Fig. 131, a b); as their position varies in different 

 species it is often indicated in specific descriptions. Some writers 

 refer to them as the openings of the epigynum. 



Even when the openings of the spermathecae are covered by 



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