[55^1 
the other a Vein, correfponding to it 3 and befides, f 
faw a Vein and an Artery lying fo clofe together/ as 
it their coats had been united. 
From the above-mentiony Artery, fmaller Vefleis 
arife acrofs the Membrane between the littie Bones, 
and when they Ve run out the breadth of three or four 
hairs, are again united in one Vein. 
Thefe fmall Veflels receive about two or three par- 
ticles of the Blood at once,efpecially if theFiPn liesftiii^ 
and confequently its little Bones clofe one to another. 
If it exercifes its little Fins in fwimming, the diftance 
between the little Bones are enlarged, the interjacent: 
Membranes ftretch'd out, and the Blood Veflels that 
run acrofs them, efpecially thofe in the Tail-fin, are 
drawn out fo as to be above twice as long as be- 
fore. 
I found it very eafy to extend the Tail-fin, and ac- 
cordingly having ftretclfd it to a breadth equal to 
what the Fifli gives it in the fwimming motion, in 
order to obferve the motion of the Blood in the thus 
extended Veflels, I foqnd that, whereas, when the 
Fifh did not move, the fmall Veflels received two or 
three partiGles in a ^reaft^ the fame Veflels now 
ftretcht out along with the Tail-fin which they run 
acrofs^ not only admit no more than one particle , 
but likewife the particles do not move fo faft as in the 
extended Veflels 5 and in fome places thefe very par- 
ticles are fo disjoyn'd, that one or two particles may 
lye in the Intervals. 
In this obfervation, I could not find that the par- 
ticles were perfeftly oval, but met with em fometimcs 
round, and fometimes in a (hapelefs figure. The oc- 
cafion oi which, to ray mind, is this : The little Vcf- 
fels being ftretch'd to an unwonted length, become 
narrower, and by confequence the particles being ve- 
ry pliant, arc prefs'd and fqueez d out of their circa! ac 
form* Tq 
