in the Spiders of the Genus Lycosa. 27 



them, on arriving at the level of the orifice, get into it, pass into 

 the venous cm-rent, and return with it in a direction opposite to 

 that which they previously followed. The same thing takes place 

 at each of the other orifices. 



These arterio-venous orifices of the legs are exactly of the 

 diameter of the blood-corpuscles. Some of the latter even tra- 

 verse them with difficulty; they are seen suddenly arrested at 

 their passage into the aperture, which they entirely obliterate ; 

 they appear to oscillate for some time" in the membranous frame 

 that embraces them, and then, the obstacle being all at once 

 surmounted, they pass quickly into the venous current. 



It is natural to inquire what is the nature of the membrane 

 in which the arterio-venous orifices are pierced. I have never 

 been able to recognize in it anything more than a simple amor- 

 phous membrane — a delicate partition which divides the calibre 

 of the leg into two parallel cavities. The arrangement here 

 would therefore be perfectly similar to that which I have else- 

 where described in the extremities of the Lsemodipoda* ; in this 

 case the pedal artery would discharge itself into the arterial 

 cavity towards the middle of the mesopodite. There may, how- 

 ever, be another interpretation : the artery may penetrate to the 

 extremity of the limb, as is usually supposed ; and in this case 

 the orifices which I have described would be pierced in the wall 

 of this vessel. If I do not adopt this hypothesis, it is because 

 I have never perceived either the walls or the pulsations of the 

 arteries beyond the middle of the mesopodite. The carpopodite 

 and the basipodite, in which the artery is distinct, do not appear 

 to present any arterio-venous orifice. 



I have examined comparatively the circulation in the legs of 

 Pholcus phalangio'ides in nearly adult individuals. The relations 

 of the arterial and venous currents are the same as in the Lycosa. 

 Unfortunately the transparency of these limbs, great as it is, is 

 not sufficient to permit the recognition of the arterio-venous 

 orifices. I can only say that in these Spiders the pedal artery 

 appeared to me to be prolonged at least to the extremity of the 

 mesopodite — that is to say, further than in the Lycosa. 



Such is the circulation of the blood in the Spiders of the 

 genus Lycosa : it is essentially lacunar, as Duges and Blanchard 

 have correctly perceived. Recently, it is true, the latter has 

 claimed for the Arachnida a far more complex circulatory system 

 than he did at first. In his ' Organisation du Regne Animal ' 

 he figures especially an unexpected abundance of vascular net- 

 works in all the tissues of the Arachnida. Venous ramifications 

 are supposed to receive the blood from these capillary nets, and 

 to pour it into the interorganal lacuna?. I venture to affirm 

 * Beobachtungen, p. 101. 



