The Internal Anatomy of Spiders 



in Tetragnatha, and five in Segestria; and according to Bertkau 

 ('75) twenty-eight in Atypus. In those spiders where the sperma- 

 thecae are detached there may be either one, two, or three con- 

 nected with the afferent duct of each side. 



The duct leading from the external opening of a spermathecae 

 to the large reservoir of this organ frequently bears a prominent 

 enlargement with densely chitinized walls (Fig. 165, g). This 

 organ was described by Schimkewitsch ('84), who states that the 

 chitinous layer of its wall is pierced by numerous pores and is 

 surrounded by an epithelium composed of very high cells, which 

 are probably glandular. 1, therefore, propose the term glands 

 of the spermathecce for these organs. As the chitinous wall of 

 these glands is often dark in colour, they may be seen through 

 the body-wall and appear as a pair of dark spots, which may be 

 mistaken for the openings of the spermathecae. 



The external openings of the afferent ducts of the spermathe- 

 cae are in the epigynum, which is described in the preceding 

 chapter. 



THE NERVOUS SYSTEM 



a. THE CENTRAL NERVOUS SYSTEM 



In fully developed true spiders, the central nervous system 

 is entirely concentrated into the cephalothorax. In early em- 

 bryonic stages there is a pair of ganglia in each segment of the 

 body; but in the course of the embryonic development a cephali- 

 zation of the ganglia takes place which results in their being 

 consolidated into a single mass surrounding the oesophagus 

 (Fig. 143). In the tarantulas, however, there is a small gang- 

 lion in the pedicel of the abdomen. 



The brain. — That part of the central nervous system that 

 lies above the oesophagus is termed the brain; from it arise the 

 optic nerves and the nerves of the chelicerae. 



The subcesophageal ganglion. — That portion of the central 

 nervous system lying below the oesophagus is termed the sub- 

 cesophageal ganglion. From this ganglion arise the nerves ex- 

 tending to the pedipalps and those extending to the legs; and 

 from the posterior end extend two large abdominal nerves. The 

 brain and the subcesophageal ganglion are not distinct, as they are 

 in insects, but are consolidated into a single mass surrounding 

 the oesophagus. 



160 



