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blood is driven in it to its fartlieft extent, that is, from A to B ; and 

 we muft name B C, a vein, becaiile, in it, the blood is returning 

 back to tlie heart. And thus it appears, that an artery and a vein 

 are one and the fame veflel prolonged or extended. 



In the part where I faw this circulation, the arteries were no lar- 

 ger than to admit a fingle particle of blood to pafs freely through 

 them : thefe particles, though in this creature they were of a fiat and 

 oval fliape, yet fometimes by reafon of the fmallnefs of the artery, 

 all'umed a kind of oblong round figure, and when the animal, by 

 being taken out of the water, grew languid, the blood in thefe very 

 minute arteries began to ftagnate, and when it again acquired mo- 

 tion, many of the globules appeared twice as long as broad, and alfo 

 pointed at their extremities. 



In another place, I faw a larger artery divide itfelf into two 

 branches, which are fliewn at fig. 3. D E, and each of thefe branches 

 returned back with a curve, as reprefented at E F and E G. Now, 

 if we denominate D E F, and D E G, arteries, becaufe, in them the 

 blood is driven outwards from the heart, it follows that F H, and 

 G I K, muft be veins, becaul'e they each bring it back towards the 

 heart. Again, not far from K, was another fmaller artery, which 

 is figured at M L ; this was united to the vein I K, fo that the 

 arteries D E G, and M L, together formed one vein at I K. In a 

 word, in this figure, H F is a vein, D E F and D E G, are arteries ; 

 G I K and K I L, are veins, and M L is an artery ; and yet we muft 

 fay, that thefe are only the fame veflels contHmed. 



In another place I faw three of the fmalleft arteries, after return- 

 ing in a curve, as before defcribed, unite in one, and thus form a vein 

 three times the fize of each artery. But all thefe three veflels with 

 their bendings wherein the circulation was performed did not occupy 

 more fpace, than could be covered by a grain of fand, 



I often perceived an artery, taking its courfe over, or croffing 



