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



called, and is cut into the back of the base of the conical diver-' 

 ticula which I have just described. The orifices of the foremost 

 pair are the largest, the next are a little smaller, and those 

 of the third pair the least of all. All these pairs serve for the 

 afflux of the blood into the heart at the moment of diastole. 

 Under the microscope, the blood- globules are seen to engulf 

 themselves in them at each dilatation. 



At this period of life the heart is not divided into several 

 chambers by internal folds or valves ; but I cannot say whether 

 this is the case also in the adult. I know that Newport and 

 Blanchard have found these valves in the heart of the Scorpion, 

 and I have no doubt that their observations are perfectly cor- 

 rect. But nothing of the kind exists, in the young Ly coses. The 

 venous orifices, which gape widely during diastole, close during 

 systole, and thus prevent the blood which they have allowed 

 to pass from returning. This closing seems to be efi'ected by 

 the action of the muscular fibres which form the margins of 

 the orifice. These fibres present one large nucleus or an agglo- 

 meration of nuclei towards the middle of the margins of each 

 orifice. At the moment of the closure of the orifice (which im- 

 mediately precedes the systole of the heart), the nuclei of the 

 opposite margins of each orifice are seen to apply themselves 

 energetically to each other. Moreover the entire wall of the 

 heart is beset with nuclei, which, however, are a little less appa- 

 rent than the above. These are no doubt the nuclei of muscular 

 cells, the presence of which is indicated by the transverse strise 

 of the wall of the heart. 



The heart receives the blood only through the six orifices 

 which I. have just described, at least unless there is a fourth pair 

 of such apertures. Indeed M. Blanchard, who represents the 

 heart in Mygale as simply cylindrical, ascribes to it four pairs of 

 atrioventricular apertures. But the place where this fourth pair 

 of apertures should be found in the Lycosae is generally so well 

 masked by vitelline granules that I have never succeeded in 

 seeing it. 



Let us now consider the issues through which the blood es- 

 capes from the heart to take its way to the organs. In the 

 first place we find the thoracic aorta originating from the ante- 

 rior extremity of the heart, as has been recognized by all the 

 anatomists who have investigated this subject. But it is only a 

 small portion of the blood that is driven by the heart into this 

 vessel. When the young Spider is placed so as to be seen in 

 profile, we perceive that it is only the cul-de-sac comprised be- 

 tween the first pair of orifices and the origin of the aorta that 

 sends its blood into that vessel. The pneumocardiac current, 

 which penetrates into the heart through these orifices, divides 



