Of the Circulation of the Blood. 5 
towards the evanefcent ones, at the extremity of the 
tail, and returned afterwards through many minute veins, 
into a larger one, as can hardly be conceived. In . the 
larger arteries he faw a continual new protrufion of the 
blood’s courfe, received from the heart; but in the fmal- 
Jer, the motion feemed equable without any fuch re¬ 
peated propulfion ; and though no colour appeared in 
the minute veflels, yet in the larger arteries and veins, 
that were near the extremity of the tail, the blood was 
plainly red. 
The exa£t magnitude this fifh appeared of to the naked 
eys, as delineated by him, is reprefented in fig. 32. Its 
tail magnified, as it appeared in the microfcope, at fig. 33. 
in which were feventeen little bones or griftles, that give 
a ftiffnefs to the tail, three of them are fhewn by the let¬ 
ters ABC, on each fide of which he faw a very open 
communication of the veins and arteries, the blood run¬ 
ning through arteries, and returning back through veins, 
which were of the fame fize, and evidently a continua¬ 
tion of the fame veffel; this was diftin&ly feen in 34 dif¬ 
ferent places, fo that in the tail of this fmall fifh could 
plainly be feen 64 blood veffels, 34 of them arteries, and 
as many veins, befides the little fpaces about D and E, 
which were not obierved. 
This will be hetter underftood by a microfcopical re- 
prefentation of part of one of thefe little griftles F H G, 
fig. 34. on each fide of which runs an artery I K and 
M N. The blood flowing rapidly from I and M, to K 
and N, their open communication with the veins K L, 
and N O, from whence it returned to L and O, fo that 
both thefe were but one continued blood veffel ; for no 
veffel can be properly called an artery beyond the pul fac¬ 
tion ; farther than which, and returning towards the 
heart, it may be called a vein; for veins, as by the pre- 
B 3 fieut 
