Circulation i?i Spiders. 407 



no dark globules occurring as in most others. 



the blood is now distinctly perceptible. The heart, as was long ago pointed 

 out, occupies the superior anterior portion of the abdomen, the blood passing in 

 laterally at the posterior part ; it contracts 53 or 54 times in a minute, the 

 muscular apparatus dragging it forwards and compressing it at the same time. 

 When it expands some of the blood seems to regurgitate, but the greater mass 

 is driven forwards through a small vessel into the cephalothorax. This vessel 

 enlarges and presents every appearance of an auxiliary heart, as attached to it 

 on each side is a cartilaginous clavicle-shaped body which is fixed anteriorly 

 and moved by lateral muscles posteriorly, and which separating and again 

 approximating drive forward the fluid. These cartilages are considerably 

 separated anteriorly, but the posterior extremity is merely separated by the 

 vessel, and is parallel to its fellow of the opposite side. The vessel in passing 

 forward from the thoracic heart ? immediately divides, a branch passing to each 

 side of the voraeriform process of the skeleton which is found beneath the cen- 

 tral thoracic point, and which gives attachment to certain muscles of the coxae; 

 it then reaches to a point about midway to the apex of the cephalothorax and 

 divides into a lash of branches, one of which joins its fellow of the opposite side 

 and runs down the centre of the forehead, its course being marked by a groove on 

 the skeleton internally, giving branches to the eyesj another branch goes down 

 the centre of the mandible or rather nearer to its outer side; and one to each of 

 the legs, palpus, jaw, &c,: that going to the posterior legs runs nearly directly 

 backwards. In tracing it down the leg we find it nearly in the middle line; it 

 terminates a little from the claw by opening directly and at right angles into 

 the vein which is of much larger size and generally lies on one side of the 

 artery in the tarsus, getting under it however at the joints; the vein being 

 larger, and subdividing and again joining, the blood moves in it much slower than 

 in the artery and apparently often stagnates until the vis a tergo produced by 

 the accumulation behind drives it on. If analogy le of much importance, this 

 settles the physiological discussion relative to an active power in the capillaries, 

 none being here at all distinguishable. The blood from the several parts, viz. 

 legs, mandibles, &c. collects in a lateral thoracic vein, the openings being at 

 right angles. This vein then passes into the abdomen at the sides of the pedicle, 

 a curious valvular structure, which I first saw last May in Lycosa saccata, being 

 placed here; it is fixed in the middle line and has its outward extremity free, 

 being of a crescentic form, and past it the current runs, a liftle eddy occuring 

 behind it as it recovers its position. The stream thtn goes directly to the pul- 

 monary sacs and thence returns to the heart. 



In Clubiona the globules arc elliptical and very long, with a dark speck about 



