322 



AR ACH N IDA ARAN E AE 



which assist in retaining the juices expressed by the chelicerae, 

 and its anterior border presents a cutting edge with a finely 

 dentated ridge called the '• serrula." 



In the female, and in the immature male, the remaining 

 joints differ little from those of the legs, except that the tarsal 

 joint is either clawless or has a single claw, which is generally 

 smooth, and is never much dentated. 



At the last moult but one the male pedipalp appears tumid 

 at the end, and after the last moult the tarsus is seen to have 

 developed a remarkable copulatory apparatus, the " palpal organ," 

 comparatively simple in some families, but in others presenting 

 an extraordinary complexity of structure. 



Palpal Organs. — Externally the essential parts of the palpal 

 organ are three, tlie " haematodocha," the " bulb," and the " style." 

 The spines and projections, or " apophyses," which often accom- 

 pany the palpal organ proper, are of secondary importance, and 

 in many spiders are entirely absent : nor is their function when 



present at all clear ; but 

 the infinite variety of 

 design which they ex- 

 hibit, and their singular 

 uniformity in all the 

 males of a species, render 

 them of the utmost value 

 as specific characteristics. 

 The " haematodocha " 

 is the portion of the 

 palpal organ attached to 

 the tarsus, and often re- 

 ceived into an excavation, 

 the " alveolus," on its 

 under surface. It is a 

 fibro- elastic bag, in ifs 

 normal collapsed state usually somewhat spirally disposed round 

 the base of the following portion, the " bulb." 



The bulb is generally the most conspicuous portion of the 

 oro-an, and is a sub-o;lobular sac with firm, though often semi- 

 transparent, integument. Its base rests upon the haematodocha, 

 and its apex is produced, often spirally, to a point which bears 

 the seminal orifice. This external opening leads into a coiled 



Fig. 179. -Diagram of palpal organ. 1, Tarsus : 

 2, bulb ; 3, receptaculum seminis : 4, its aper- 

 ture ; 5, style ; 6, haematodocha ; 7, alveolus ; 

 8, tibia. 



