[ J 52 ] 
to imagine, that their Fins may poflibiy be the Or- 
gans more immediately fenfiblc of the flighted Mo- 
tions in the Medium wherein they dwell. The 
Ciuious, who have obferved the Fins of Fifhcs with 
the Microfcope,^ find them to be compofcd of infi- 
mtely fine Veflels, Arteries, Veins, Mufelcs, and 
membranous Fibril! a , whofc Structure feems more 
delicate than is needfary for Parts that ferve only as 
Oars to waft the Fifh along. This however I de- 
hre you to regard as a mere Conjecture, for which 
the neceflary Proofs are wanting. 
At other times, if, by ftriking on the Top of the 
Jai with a fmall Key, the Stroke or Tremor has 
been a little more violent, the Fifh would fhut down 
their back Fins in a Moment, and remain motionlefs 
at -the Bottom of the Glafs. The fudden Appear- 
ance of my Hand at the Top of the jar would like- 
wiie produce the fame EfFcdl ; but Noifes made 
near them feemed to give them no Djfturbance. 
Thefe Experiments I have often repeated before 
feveral of my Acquaintance, as well as by myfclf in 
private, and feldom found them to vary much. But 
Fifh newly taken out of Ponds, or Rivers, muff not 
be expected to perform all I here relate : For they, 
lixe birds juft raken in the Fields, and put in Cares, 
arc thrown into Confufion at the Approach of any 
thing, and endeavour continually to retrain their 
Freedom. 
If the Eyes of Fifhcs be carefully examined, when 
fwimming in a glafs Vcfle'l, the Cornea or black 
Uvea of their Eyes may be feen, fometimes ad- 
vancing forwards, and at other times retiring back, 
juft as their Sight is directed to near or diftant Ob- 
jects, 
