26 M. E. Claparede on the Circulation of the Blood 



from the ophthalmic lacuna, but chiefly from deep-seated median 

 lacunae ; it becomes enlarged momentarily at one place or an- 

 other, and it is at these points that the blood-corpuscles emerge 

 from the depths. The blood is poured out into these median 

 lacunas by the inner and ascending branch of the artery of the 

 protognath. 



To complete this picture of the circulation in the Lycosa, it 

 now only remains for me to describe the course of the blood in 

 the legs. The pedal arteries and the artery of the deutognath 

 above mentioned are easily seen penetrating into the extremities. 

 Each artery has its distinct walls and its regular pulsations, and 

 we may trace it readily through the coxopodite and the basi- 

 podite to the middle of the mesopodite. Beyond this point I 

 have never succeeded in recognizing either its walls or its pulsa- 

 tions. At the first glance, the arterial blood in the following 

 joints seems to move only in intermuscular lacunae. It appears 

 to be in immediate juxtaposition with the venous blood moving 

 in the opposite direction, although the two currents never seem 

 to interfere with one another. The artery, as long as it has 

 proper walls, occupies the centre of the leg, and is bathed on 

 all sides by the venous blood. But beyond the middle of the 

 mesopodite the arterial current occupies the side of flexion, and 

 the venous current that of extension. 



It is soon seen that only a small part of the blood conveyed 

 into the leg by the artery finds its way to the extremity of the 

 limb. The greater part of the blood-corpuscles pass into the 

 venous current without penetrating so far into the foot. More- 

 over a careful examination quickly shows that the passage of the 

 blood-globules from the arterial into the venous current occurs 

 at perfectly determinate points. These are five in number, and 

 present themselves in the form of circular, or, rather, oval spots, 

 when the limb is examined either on the side of flexion or ex- 

 tension. The first is situated close to the peripheral margin of 

 the mesopodite ; the second occupies a precisely similar position 

 in the carpopodite ; the third is placed in the propodite, but at 

 a rather greater distance from its peripheral extremity ; the 

 fourth belongs to the first dactylopodite, but is still further re- 

 moved from the peripheral margin of that joint; and the fifth is 

 placed nearly in the middle of the second dactylopodite. These 

 clear spots, with their outlines perfectly distinct and free, are 

 openings in a membrane which separates the arterial from the 

 venous current. If we pay particular attention to one of these 

 apertures — for example, that in the propodite, at the same time 

 noting the mode in which the arterial current behaves at this 

 point, we see that part of the blood-corpuscles continue their 

 course directly to pass into the dactylopodite, but that some of 



