The External Anatomy of Spiders 



writers. From the published observations it appears that the male spins a delicate 

 web upon which he emits the seminal fluid; after which the fluid is taken up by 

 the palpus. 



The genital appendage of the palpus of the male is exceedingly complicated 

 in structure in the more specialized spiders, as in the Argiopidae; but it is com- 

 paratively simple in some of the more generalized families. A few illustrations 

 of the simpler forms will be given here. 



The Filistata Type of Palpus. — in Filistata bibernalis, which is a very 

 common house spider in the South, is found the most simple type of male palpus 

 that I have seen among spiders. In the males of this species, the distal end of the 

 last segment of the palpus, the tarsus, contains a coiled tube (Fig. 93); this is the 

 receptaculum seminis. 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. 93, a);* this cavity is the alveolus (Menge '66). 

 The slender prolongation of the bulb, which contains the terminal portion of the 

 receptaculum seminis is the embolus; the embolus is often termed the style. 



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 receptaculum seminis. Regarding the origin of the receptaculum 

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

 intima of a trachea, indicates that it is merely an invagination of the body-wall. 

 In its primitive form, it was probably a cup-like depression in the tip of the tarsus. 



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

 taculum seminis consists of three quite distinct parts: first, the proximal end of it, 

 the fundus, is enlarged so as to form a pouch, the wall of which is more delicate 

 than that of the other parts (Fig. 94, 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 reservoir, is a large coiled tube occupying the middle 

 division of the genital bulb (Fig. 94, 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 a slender tube traversing the apical division 

 of the bulb (Fig. 94, ej. d.) the wall of this duct is often dark in colour, which 

 renders it easy to trace the course of the duct in an expanded bulb. 



The tracing of the course of the ejaculatory duct is often the only method by 

 which the embolus can be recognized in a complicated palpus; for when the em- 

 bolus is small or when it is lamelliform a slender apophysis may be mistaken for it. 



After the stage represented by Filistata had been reached, a shifting in the 

 position of the bulb occurred in most spiders. Instead of occupying a terminal 

 position, at the tip of the tarsus, it has moved to one side of the tarsus in all spiders 

 known to me except Filistata. In the tarantulas and in Hypochilus thorellii, the 

 most generalized in many respects of the true spiders, the genital bulb is nearly 

 terminal, but is, nevertheless, distinctly on one side of the tarsus (Fig. 95). In 

 other spiders it has moved to a greater or less extent toward the base of the 

 tarsus, which it has nearly reached in many, as for example in Loxosceles rujescens 



(Fig. 9 6 )- 



In Hypochilus (Fig. 95) and in Loxosceles (Fig. 96), the alveolus is compar- 

 atively small; but in many spiders it is large, resulting in the tarsus being more or 

 less cup-like in form; this is shown in some of the figures of the more specialized 

 palpi given later. This cup-like form of the tarsus, as distinguished from its 

 appendage, the genital bulb, suggested for it the name cymbium, which is the 

 classical name of a small drinking vessel. 



*In the figures of palpi of males given in this chapter, uniform abbreviations are used for the 

 names of the parts. A list of these is given at the close of the account on page 121. 



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