The Internal Anatomy of Spiders 



In certain generalized spiders, as Atypus, Segestria, Dysdera, 

 Tetragnatha, and others, the spermathecae are diverticula of the 

 vagina. In these cases there is only a single external opening 

 of the reproductive organs. But in most spiders, the sperma- 

 thecae are more or less detached and have separate external 

 openings. In these cases there are 

 three external openings of the repro- 

 ductive organs, the opening of the 

 vagina, and a pair of openings of the 

 afferent ducts leading to the sper- 

 mathecae. In this type of reproductive 

 organs, a tube connects the sperma- 

 thecae of each side with the vagina. 

 Figure 165 is a diagrammatic repre- 

 sentation of this type. 



The ovaries. — The ovaries are situ- 

 ated in the abdomen below the intes- 

 tine and above the longitudinal ventral 

 muscles (Fig. 143). They are sur- 

 rounded by silk glands and the ali- 

 mentary tubules, and are two broad 

 tubes bearing numerous ovarian fol- 

 licles and appearing like a cluster of 

 grapes. The free ends of the ovaries 



are sometimes .grown together so as to pro- 

 duce a ring-like structure (Fig. 166). 



The size of the ovaries varies greatly, de- 

 pending on the state of the development of the 

 eggs. Just before the egg-laying period, they 

 become greatly distended and occupy a consider- 

 able part of the abdominal cavity. 



The oviducts. — Each ovary opens through 

 a short oviduct; and these in turn open into a 

 common pouch, the uterus, which leads to the 

 vagina; and the vagina opens on the middle line 

 of the body in the epigastric furrow. 



The spermatheca:. — The spermathecae vary 

 in number. In those spiders where the sperma- 

 thecae are diverticula of the vagina, as described above, there 

 are, according to Engelhardt ('10), two in Pachygnatha, three 



Fig. 165. DIAGRAM OF THE 

 INTERNAL REPRODUCTIVE 

 ORGANS OF THE FE- 

 MALE OF ARANEA 



0, ovary od, oviduct u, uterus 



v, vagina s, spermatheca 



os, opening of the spermatheca 



1, tube connecting the spermatheca 



with the vagina 



g, gland of the spermatheca 



ig. 166. RING- 

 LIKE OVARIES 

 OF A SPIDER 



0, ovaries 

 od, oviduct 

 s, spermathec 

 (after Lang) 



159 



