in the Spiders of the Genus Lycosa. 21 



place if the views of M. Blanchard with regard to his supposed 

 pneumocardiac vessels and the pericardium were well founded. 



It is true that there are_, in some degree, pneumocardiac ves- 

 sels, and even a kind of pulmonary veins. These vessels, how- 

 ever, have the following peculiarities : — they are very wide, they 

 never communicate directly with the arteries or with the heart, 

 and both their extremities open into interorganal lacunse. I 

 shall call them sinuses, desiring to indicate thereby that they 

 incontestably possess proper walls. 



I shall describe these sinuses, commencing with those whose 

 office it is to conduct the blood to the respiratory organs, and 

 concluding with those which convey the oxygenated blood to 

 the heart. We have seen that the posterior region of the body 

 presents a very large lacuna, occupying especially the pygidiura 

 and the spinners. The blood which fills this lacuna passes at 

 the ventral part of the abdomen into two sinuses — the longitu- 

 dinal sinuses of the abdomen — which convey it forward. These 

 two sinuses are nearly parallel to each other, and their walls are 

 of a silky whiteness when they are seen by incident light. The 

 blood flows in them constantly from behind forwards. These 

 two sinuses occupy the whole length of the abdomen, and unite 

 in a median sinus at its base. In their anterior portion, how- 

 ever, these sinuses present a circulation exactly opposite to that 

 just described. The blood there always travels from before back- 

 w^ard : this is because at this part they carry the blood of the 

 thoracic lacunse. In reality these longitudinal sinuses of the 

 abdomen are composed of two parts, which, anatomically, form 

 the direct continuation the one of the other, but which never- 

 theless convey the blood in opposite directions. The point of 

 junction of these two parts is the inner and posterior angle of 

 the lung ; here each of the longitudinal sinuses gives origin to 

 a transverse process, which may be called the posterior pulmo- 

 nary sinus, as it borders the posterior margin of the lung. The 

 two currents of the longitudinal sinus flow into this transverse 

 sinus, in which they mix together ; on arriving at the outer and 

 posterior angle of the lung, the stream of blood changes its 

 direction, almost at a right angle, to form what may be called 

 the lateral pulmonary sinus, which follows the outer margin of 

 the lung. This sinus then bends towards the upper part of the 

 abdomen to open into the pericardiac lacuna, nearly at the level 

 of the first pair of lateral orifices. Most of the blood-globules 

 pass from the posterior to the lateral pulmonary sinus by de- 

 scribing the angle that I have just described; some, however, 

 cut this angle by ghding obliquely over the lung. This proves 

 that the posterior and lateral pulmonary sinuses are only the 

 margins of a large sinus in which the entire lung is immersed. 



