The External Anatomy of Spiders 



The lung-slih. — Of these there are either one or two pairs. 

 The first pair, which is always present except in one small, exotic 

 family (Caponiidae) is situated one at each end of the epigastric 

 furrow. In the tarantulas and in the family Hypochilidae there 

 is a second pair of lung-slits behind the first (Fig. 129). 



The tracheal spiracles. — In the true spiders except the family 

 Hypochilidae there are ordinary tracheae in addition to the book- 

 lungs. In most cases the ordinary tracheae open by a single 

 spiracle, which is usually situated on the middle line, a short 

 distance in front of the spinnerets; but sometimes this single 

 spiracle is near the middle of 

 the ventral aspect of the ab- 

 domen. In a few spiders there 



r t 



/' 



/ 



iS 



A 



Fig. 129. VEXTRAL ASPECT OF 

 ABDOMEN OF A TARANTULA 

 e, epigastrium 

 ef, epigastric furrow 



Fig. 130. DYSDERA INTERRITA, 



A TRUE SPIDER WITH A PAIR 



OF TRACHEAL SPIRACLES 



BEHIND THE LUNG-SLITS 



is a pair of tracheal spiracles situated just behind the lung-slits; 

 these can be distinguished from lung-slits by the absence of 

 external indications of book-lungs. Compare Figs. 129 and 130. 



The epigynum (e-pig'y-num). — The internal reproductive 

 organs open on the middle line of the abdomen in the epigastric 

 furrow. In the male the opening is simple, without any intro- 

 mittant organ, the palpi taking the place of such an organ. In 

 the female the two ovaries open by a common opening, which in 

 some spiders is not accompanied by any specialized chitinous 

 structure; this condition exists in Tetragiuiiha and other genera. 

 But in most of the true spiders (Argiopoidea) there is connected 

 with this outlet a more or less complicated apparatus, which is 

 termed the epigynum. 



120 



