The External Anatomy of Spiders 



The Tarantula Type of Palpus. — In those spiders that are commonly 

 known in this country as tarantulas, and which represent the more generalized 

 of the two principal divisions of the order Araneida, there exists a comparatively 

 simple type of palpus; but in none of them that 1 have seen, or of which 1 have seen 

 figures, is it as generalized as is the palpus of Filistaia. 



In the palpi of the tarantulas, the genital bulb has migrated to one side of the 

 tarsus; but it is still near the tip of this segment of the palpus (Fig. 97). A striking 

 feature of the bulb is that it is divided into two distinct segments. The smaller 

 basal segment may be termed the basal division of the bulb (Fig. 97, b. d.). The 

 larger segment consists of two parts: a large stout part, which may be termed 

 the middle division of the bulb (Fig. 97, m. d.), and a slender terminal portion, 

 which may be termed the apical division of the bulb (Fig. 97, a. d.) ; there is, however, 



no distinct line between the middle and the apical 



divisions, the one gradually merges into the other; 



but in the more specialized palpi these two divisions 



are distinctly separated. 



In the articulating membrane which joins the 



m. d. 



Fig. 97. TARSUS OF 

 EURYPELMA 



Fig. 98. GENITAL BULB OF 

 EURYPELMA CALIFORMCUM 



bulb to the tarsus, there is on one side a distinct sclerite, which can be 

 seen by removing the bulb from the alveolus (Fig. 98, pet.); this is doubt- 

 less homologous with what has been termed the petiole in more specialized palpi. 



The greater part of the wall of the bulb in the tarantula type of palpus is 

 very densely chitinized but there is a longitudinal area on the concave side of the 

 middle and apical divisions which is comparatively soft (Fig. 98, p.p.); it may be 

 that this part is distended by blood pressure at the time of pairing as is the ha?ma- 

 todocha in the more specialized palpi; but upon this point I have no data. This 

 soft strip may correspond to that portion of the spiral type of embolus, described 

 later, thai I have designated the pars pendula. 



I in Palpus of Loxosceles. — In certain genera of the true spiders, the palpi 

 are as simple as in the tarantula type. In Loxosceles of the family Scytodidae, 

 for example (Fig. 96), although the bulb has migrated nearly to the base of the 

 tarsus, the bulb itself is very simple in structure 1 he basal division of the 

 bulb is inconspicuous; the middle division is nearly spherical, and the apical 

 division is long and slender. Here the receptaculum seminis is differentiated 

 into the three parts described above; the reservoir is large, while the ejaculatory 

 duct is very slender. 



1 ill. Palpus of Dysdera. — In the family Dysderidae two quite distinct 

 types of palpi occur. In Artadna the palpus resembles very closely thai of Loxo- 

 sceles; but in Dysdera it is of a very different form (Fig. 99); this is due to the Fart 

 that the apical division of the bulb is not slender, and is sharply differentiated 

 from the middle division, its wall being much less densely chitinized. Bui there is 

 on each margin a distinct sclerite; and this part of the bulb bears distinct apoph- 

 yses. At the tip of the apical division there appears to be the beginning ol ! 

 separation into embolus anil conductor. 



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