TRACHEATA 4It 
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 Zpeira 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, ete. The blood is 
ultimately collected in various sinuses, one of which is con- 
tinuous with the spaces in the lamellae of the lungs. From 
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 
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 
