264 ARTHROPODA [CH. 



masses of the digestive and reproductive glands. The oesopha- 

 gus, which leads from the mouth, opens into a strong sucking 

 "stomach," which, like the stomach of the Crayfish, is really a 

 stomodaeum. This is attached by muscles to the chitinous exo- 

 skeleton, and when the muscles contract its cavity is enlarged and 

 thus a sucking action is induced at the mouth (Fig. 118). Behind 

 this is an endodermic portion of the alimentary canal which gives 



14 18 



Fio. 118. Diagram of a Spider, Epeira diademata, showing the arrangement 

 of the internal organs x about 8. From Warburton. 



1. Mouth. 2. Sucking stomach. 3. Ducts of liver. 4. Malpighian 

 tubules. 5. Stercoral pocket. 6. Anus. 7. Dorsal muscle of 

 sucking stomach. 8. Caecal prolongation of stomach. 9. Cerebral 

 ganglion giving off nerves to eyes. 10. Sub-oesophageal ganglionic 



mass. 11. Heart with three lateral openings or ostia. 12. Lung-book. 

 13. Ovary. 14. Acinate and pyriform silk glands. 15. Tubuliform 

 silk gland. 16. Ampulliform silk gland. 17. Aggregate or dendriform 

 silk glands. 18. Spinnerets or mammillae. 19. Distal joint of 



chelicera. 20. Poison gland. 21. Eye. 22. Pericardium. 



23. Vessel bringing blood from lung sac to pericardium. 24. Artery. 



off two caeca or blind tubes which project forwards ; from each of 

 these four smaller pockets arise one projecting into the base of each 

 walking leg ; behind these comes an intestine which traverses the 

 abdomen and is further provided with a number of ducts which 

 collect the products of a very capacious digestive gland or "liver." 

 The hinder portion of this intestine is swollen up into a pouch 

 called the stercoral pocket. Following the intestine comes 

 a short proctodaeum lined by ectoderm which ends in an anus 

 situated close behind the spinnerets. 



Spiders possess two kinds of organs which excrete waste nitro- 

 genous material : (i) the coxal glands, which are coelomiducts, like 

 the "nephridia" of Peripatus, i.e., glandular tubes running between 

 a reduced coelom and the exterior, and (ii) Malpighian tubules, a 



