1910] The Palpi of Male Spiders 163 



ders. In the males of this species, the distal end of the last 

 segment of the palpus, the tarsus, contains a coiled tube (Fig. 1) ; 

 this is the receptacidum seminis (Wagner '87). The proximal 

 portion of this tube is slightly enlarged and ends blindly; the 

 distal part is slender and extends through a slender, twisted 

 prolongation of the tarsus ending at its tip by an open mouth. 

 The modified terminal portion of the tarsus, which contains the 

 receptaculum seminis, is the genital bulb. By looking directly 

 at the tip of the palpus, instead of at one side of it, it can be 

 seen that the base of the bulb is situated in a cavity in the end 

 of the main part of the palpus (Fig. 1, a.). This cavity is the 

 alveolus (Menge 'GO). The slender prolongation of the bulb, 

 which contains the terminal portion of the receptaculum 

 seminis is the embolus (Menge '66; style, Simon, '92). Except 

 ing the specialization of the distal end of the tarsus, the segments 

 of the palpus of Filistata resemble quite closely the correspond- 

 ing segments of a leg, the relative length of the femur, patella, 

 and tibia being quite similar; there is not the shortening of the 

 tibia, which is so marked in many of the specialized forms, as 

 in Aranea for example. 



A study of the palpus of Filistata gives a clue to the probable 

 course of the evolution of the genital bulb. It is evident that 

 the bulb is a specialization of the tip of the tarsus, and its most 

 striking feature is the presence within it of the coiled recepta- 

 culum seminis. Regarding the origin of the receptaculum 

 seminis, the fact that it is furnished with a transversely striated 

 intima, hke the intima of a trachea, indicates that it is merely 

 an invagination of the body-wall. In its primitive form, it 

 was probably a cuplike depression in the tip of the tarsus. 



In its most perfect form, as seen in the more specialized 

 spiders, the receptaculum seminis consists of three quite dis- 

 tinct parts: first, the proximal end of it, the fundus, is enlarged 

 so as to form a pouch, the wall of which is more deHcate than that 

 of the other parts (Fig. 2, fu.) ; I have not been able to see 

 taenidia in the intima of this part, and infer that it serves as a 

 compressible bulb; second, the intermediate portion, the reser- 

 voir, is a large coiled tube occupying the middle division of the 

 genital bulb (Fig. 2, res.), in this part the taenidia of the intima 

 are well-developed and are sometimes very prominent; third, 

 the terminal portion constitutes the ejaculatory duct; this is the 

 slender tube traversing the apical division of the bulb (Fig. 2, 



