33- 



ARACHNIDA' — ARANEAE 



arteries leave the heart, the principal one, or " aorta," plunging 

 downward and passing through the pedicle to supply the cephalo- 

 thorax. Besides this, there is a caudal artery at the posterior 

 end, and three pairs of abdominal arteries, which proceed from 

 the under surface of the heart, and the ramifications of which 

 supply, in a very complete manner, the various organs of the 

 abdomen. The heart is not divided up into compartments. The 

 anterior aorta passes through the pedicle, above the intestine, and 

 presently forks into two main branches, which run along either 

 side of the sucking stomach, near the front of which they bend 



Fig. 186. — Diagram of a Spider, Epeira dUtdemata, showing the arrangement of the 

 internal organs, x about 8. 1, Mouth; 2, sucking .stomach; 3, ducts of liver; 

 4, so-called Malpighian tubules ; 5, stercoral pocket ; 6, anus ; 7, dorsal muscle of 

 sucking stomacli ; 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-sac ; 13, ovary ; 14, acinate and pyriform silk-glands ; 

 16, tubuliform silk-gland ; 16, ainpuUiform silk-gland ; 17, aggregate or deudriform 

 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 peri- 

 cardium ; 24, artery. 



suddenly downwards and end in a " patte d'oie," as Causard ^ 

 expresses it — a bundle of arteries which proceed to the limbs 

 (Fig. 185). Wliere the downward curve begins, a considerable 

 artery, the mandibulo-cephalic, runs forward to supply the cheli- 

 cerae and the head region. We have omitted certain minor 

 branches from the main trunks which supply the thoracic 

 muscles. The nerve-mass receives fine vessels from the " patte 

 d'oie." 



There are no capillaries, but the blood is delivered into the 

 tissues and finds its way, by irregular spaces or " lacunae," into 

 certain main venous channels or " sinuses." There are three such 



' Eecherches sur I'appareil cireulatoire des AranHdes. Lille, 1896. 



