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



The blood-globules never penetrate between the leaflets of the 

 respiratory organ ; and, no doubt, it is the plasma of the blood 

 that is endowed with the function of absorbing oxygen and 

 emitting carbonic acid. 



In consequence of the arrangement of sinuses which I have 

 just described, the greater part of the blood passes through the 

 lung before returning to the heart. This is the case with all the 

 venous blood of the cephalothorax arriving by the anterior part 

 of the median longitudinal sinuses; it is also the case with a 

 great part of the blood returning from the pygidian lacuna 

 through the posterior part of these sinuses. It is possible that 

 the quantity of abdominal blood arriving at the lung may be 

 still greater; in fact each longitudinal sinus of the abdomen 

 receives, about the middle of its length, a transverse sinus, which 

 probably brings to it a new affluent. Nevertheless I have never 

 been able to ascertain the direction of the circulation in this 

 sinus ; it may be that it conveys non-oxygenated blood derived 

 from the longitudinal sinus into the pericardiac lacuna. How- 

 ever this may be, it seems probable that a great part or even 

 nearly the whole of the blood of the pericardiac lacuna behind 

 the first pair of lateral orifices has not passed through the lungs. 

 Indeed, it must not be forgotten that the blood moves from be- 

 hind forwards in this lacuna. All the blood that returns from 

 the lungs penetrates into the heart through the first pair of 

 lateral orifices. 



The longitudinal sinuses of the abdomen, in which the blood 

 is seen in rapid motion, appear to have hitherto escaped the no- 

 tice of nearly all observers. It is probable, however, that they 

 might be demonstrated even by the scalpel in the larger species. 

 Their position, indeed, is easily determined ; they repose exactly 

 upon the longitudinal muscular bands which Treviranus* was 

 the first to indicate, which were subsequently described by 

 Brandt f as tendons, and which recent anatomists, M. Blanchard 

 included, have seen like their predecessors. Duges alone seems 

 to have had some knowledge of these sinuses. He says | : "In 

 the common Epe'ira of Walckenaer the skin of the abdomen is 

 very transparent and slightly coloured soon after a moult, and 

 then the whole abdomen may be seen banded transversely and 

 obliquely by very superficial vascular ramifications, starting from 

 the whole length of the lateral and superior margins of the 

 heart and from its posterior extremity. They are seen less 

 distinctly in the Epe'ira diadema. These innumerable vessels, 



* hoc. cit. p. 45. 



t Recherches sur l'Anatomie des Araignees (Ann. Sc. Nat. 2 e ser. 1840, 

 tome xiii. p. 180. 

 J hoc. cit. p. 359. 



