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
