248 ON GENERATION. 



excluded from the air. The vein to which this mucor attaches, 

 as I have said, is the vena cava, descending along the spinal 

 column, as my subsequent observations have satisfied me. And 

 if you carefully note the order of contraction in the pulsating 

 vesicles, you may see the one which contracts last impelling its 

 blood into the root of this vein and distending it. 



Thus there are two manifest contractions and two similar 

 dilatations in the two vesicles which are seen moving and pul- 

 sating alternately; and the contraction of the one which precedes 

 causes the distension or dilatation of the other ; for the blood 

 escapes from the cavity of the former vesicle, when it contracts, 

 into that of the latter, which it fills, distends, and causes to 

 pulsate ; but this second vesicle, contracting in its turn, throws 

 the blood, which it had received from the former vesicle, into 

 the root of the vein aforesaid, and at the same time distends 

 it. I go on speaking of this vessel as a vein, though from its 

 pulsation I hold it to be the aorta, because the veins are not 

 yet distinguished from the arteries by any difference in the 

 thickness of their respective coats. 



After having contemplated these points with great care, and 

 in many eggs, I remained for some time in suspense as to the 

 opinion I should adopt; whether I should conclude that the 

 concrete appended globular mass proceeded from the colliqua- 

 ment in which it swam, becoming a compacted and coagulated 

 matter in the way that clouds are formed from invisible vapour 

 condensed in the upper regions of the air ; or believe that it 

 took its rise from a certain effluvium exhaled from the san- 

 guineous conduit mentioned, originating by diapedesis or trans- 

 udation, and by deriving nourishment from thence, was enabled 

 to increase ? For the beginnings of even the greatest things 

 are often extremely small, and, by reason of this minuteness, 

 sufficiently obscure. 



This much I think I have sufficiently determined at all 

 events, viz. that the puncta salientia and meatus venosi, and 

 the vena cava itself, are the parts that first exist ; and that the 

 globular mass mentioned afterwards grows to them. I am 

 further certain that the blood is thrown from the punctum 

 saliens into the vein, and that from this does the corpuscle in 

 question grow, and by this is it nourished. The fungus or 

 mucor first originates from an effluvium of the vein on which 



