TRACHEA TA 411 



as in Argyroneta, the tracheal stigmata are situated just behind 

 the pulmonary, in the same position as the second pair of lung 

 sacs in the Tetrapneumones. 



The heart in Epeira is separated from the dorsal integu- 

 ment as well as from the intestine by some of the lobes of the 

 liver ; it lies in a pericardium, and is confined to the abdomen. 

 The heart is described as giving off an anterior and a posterior 

 aorta, and four pairs of lateral vessels. Three pairs of lateral 

 ostia admit the blood which has collected in the pericardium 

 into the heart ; this contracts, and forces it through the blood- 

 vessels. The anterior aorta splits in the thorax, and each half 

 bends backwards and downwards to supply the legs and 

 neighbouring parts. From the summit of each bend a cephalic 

 artery runs forward to supply the organs in the head. The 

 course of the lateral vessels in the abdomen cannot be easily 

 followed, as the vessels have very thin walls, and soon lose 

 themselves in the tubules of the liver, etc. The blood is 

 ultimately collected in various sinuses, one of which is con- 

 tinuous with the spaces in the lamellae of the lungs. Trom 

 these organs it is returned to the pericardium, and thence to 

 the heart. 



The blood is colourless, and contains relatively few large 

 round corpuscles, but many amoeboid ones. 



The mouth is guarded on each side by the maxillary process 

 of the pedipalpus, and in front and behind by an upper and 

 lower lip ; it is a transverse slit and leads into the pharynx, 

 a narrow tube lined with chitin which passes perpendicularly 

 upwards and forms a right angle with the next section of the 

 alimentary canal, the oesophagus. This tube is also lined with 

 chitin, it is encircled by the nerve ring and opens into an ex- 

 pansion known as the sucking-stomach. The lumen of the 

 latter is triangular in cross section, and its walls are strengthened 

 by chitinous plates ; strong muscles unite the dorsal wall of 

 this organ with the chitinous integument of the tergum, and 

 similar muscles pass between its ventro-lateral walls and the 

 J endosternite ; the contraction of these muscles enlarges the 

 lumen of the organ, and the juices of the prey are thus sucked 

 into the digestive canal of the spider. 



The sucking-stomach communicates with the very small 



