The External Anatomy of Spiders 



A summary of the parts of the tarsus in the more generalized types of palpi 

 of males is shown by the following table: 



Body of tarsus or cymbium, containing the 



alveolus 

 Genital bulb 



Internal parts 



Receptaculum seminis 

 Fundus 

 Reservoir 

 Ejaculatory duct 

 External parts 

 Petiole 



Basal division 

 Middle division 

 Apical division or embolus 



THE INTERMEDIATE TYPES OF PALPI 



There are palpi which hold an inter- 

 mediate position as regards complexity of 

 structure between the comparatively simple 

 tarantula type and the exceedingly complex 

 forms to be described later. These inter- 

 mediate types occur in widely separated 

 portions of the araneid series; but agree in 

 their more essential characteristics; for sake 

 of brevity, I will discuss only a few ex- 

 amples of the intermediate types; and will 

 then pass to a description of forms in which 

 the maximum number of parts are found. 



The most important characteristic of 

 these intermediate types is that the apical 



division of the bulb is separated into two, more or less nearly, parallel parts. 



One of these parts contains the ejaculatory duct of the receptaculum seminis, 



this is the embolus; the other is intimately associated with the embolus and is 



known as the conductor of the embolus, or 



the conductor of the style, or, simply, as 



the conductor. 



A comparatively simple example of 



this group of palpi is that of Atypus 



bicolor. Here the terminal part of the 



conductor is a broad concave plate (Fig. 



100), in which the terminal portion of the 



embolus rests. 



A more complicated form of the 



apical division of the bulb exists in 



Hypochilus thorellii (Fig. 95). Here the 



embolus is coiled about the conductor, 



the terminal part of which is concave so 



as to support the terminal portion of the 



embolus; the tip of the conductor bears 



a delicate membranous flap. 



In Hypochilus the tarsus bears a 



branch which supports a prominent bunch of bristles (Fig. 95, p. c); this may 



be a rudimentary form of paracymbium, a part that is well-developed in Pachy- 



gnatha. 



A somewhat similar condition exists in Pachygnatha (Fig. 101). Here the 



proximal part of the embolus is coiled about the conductor, which is a broad 



twisted plate; and the terminal portion of the embolus is supported by the corre- 

 sponding part of the conductor. When at rest the apical division of the bulb 



Fig. 99. PALPUS OF DYSDERA 

 INTERRITA 



..■cym. 



cmb.- 



con. 



mm 



mm 



'~ t. 



m 



Fig. 100. 

 TARSUS OF ATYPUS BICOLOR 



I IO 



