XIII REPRODUCTIVE AND NERVOUS SYSTEMS 333 



in the cephalothorax, one median and the others lateral, con- 

 siderably dilated in front, in the region of the eyes, and connected 

 by transverse passages. By these the blood is brought back 

 through the pedicle to the lung-books. In the abdomen also 

 there are three main sinuses, two parallel to one another near the 

 lower surface, and one oeneath the pericardium. These likewise 

 bring the blood to the lung-books, whence it is conducted finally 

 by pulmonary veins (Fig. 186) back to the pericardial chamber, 

 and thus, by the ostia, to the heart. 



The Spider's blood is colourless, and the majority of the 

 corpuscles are " amoeboid," or capable of changing their shape. 



Generative System. — The internal generative organs present 

 no great complexity, consisting, in the male, of a pair of testes 

 lying beneath the liver, and connected by convoluted tubes, the 

 " vasa deferentia," with a simple aperture under the abdomen, 

 between the anterior stigmata. 



The ovaries are hollow sacs with short oviducts which presently 

 dilate to form chambers called " spermathecae," which open to the 

 exterior by distinct ducts, thus forming a double orifice, fortified 

 by an external structure already alluded to as the " epigyne." 

 The eggs project from the outer surface of the ovary like beads, 

 connected with the gland ])y narrow stalks, and it was not at 

 first clear how they found their way into the interior cavity, but 

 it has been ascertained that, when ripe, they pass through these 

 stalks, the empty capsules never presenting any external rupture. 



The palpal organs have already l^een described. The sperma- 

 tozoa, when received by tliem, are not perfectly elaborated, but 

 are contained in little globular packets known as " spermato- 

 phores." 



Nervous System.^ — The Spider's central nervous system is 

 entirely concentrated in the cephalothorax, near its fioor, and 

 presents the appearance of a single mass, penetrated by the 

 oesophagus. It may, however, be divided into a pre-oesophageal 

 portion or brain, and a post-oesophageal or thoracic portion. 



The brain supplies nerves to the eyes and chelicerae, while 

 from the thoracic mass nerves proceed to the other appendages, 

 and through the pedicle to the abdomen. The walls of the 

 oesophagus are closely invested on all sides by the nerve-sheath 

 or neurilemma. 



Sense Organs. — Spiders possess the senses of sight, smell, and 



