( 3 ?o ) 
blddder,the ftoiiiach prefently fwelled; So that it fcems in that 
Filh the air paflfes freely both wayes. Poflibly, the Filh while 
alive may have an ability to raife up this valve, and let out 
air uponO-CcafioD, which yejt I doubt of, becaufe other A- 
nimals have no fuch faculty of opening any valves made to ffop 
the reflux of fluids. But I\ verily think , ihere is in the coat 
of this bladder a mufculous power to contraft it when the Fifli 
liftsiFor, in many Fiffies it is very thick and opake, like the 
coat of an Artery (which hath, ^sDt. Willis obftrves, fiich a 
mufcular faculty ) as for example in all the Cod-kind; in 
fomc, v* g. the Hakey called in Latin Merlucim , it is inwardly 
covered with a red carneous fubftance, which I take to be muf- 
culous flefli ; ia others,it is forkedat the top, and toeach horn 
hath a mufcle affixed. Now the mufculous force need not be 
great , being ftil I aflifted by the water as the Fifli defcends ; 
the prelTure of the water being much greater at the bottom- than 
at the top , as appears by theafcending bubble* But whereas 
it is faid, Perhaps the Fifli can by its fides or fome other defence 
keep off the preffure of the water , and give the air leave to di- 
late ic felf: It may beobjcfied, ifi^ can do fo, what needs 
then any air-blacWer f the cavity of the abdmen may (erve the 
turn. To which I anfwer , that this power of dilating the ah- 
domenhy xh^mw^cXes may aflift Fiflies to rife, whofe natural 
place is toward the bottom; and the Air comprefled in the 
bladder dilating it felf as the Fifli afcends, facilitates the a- 
ftion of the mufcles. But thofe Fiflies that defcend by con- 
tradling the bladder, letting the contrafling mufcle ceafe to ad, 
will rife again of their own accord, the Air within dilating 
it felf, as we fee in glafs bubbles by compreflion of the Air in 
them defcending, which as foon as the force is removed af- 
C)end without more ado. Befides the flat Fifljes I before 
mentioned, all the carcilagineous kind, as well fiat as long, 
want fwimming bladders; What courfc they ufe to afcend 
and defcend in the water, I know not. Many of the Eel-kind 
fnot all ) have fwimming bladders ; yet can they hardly raife 
therofelvesin the water, by reafon of the length and weight 
of their tails; I fuppofe,the Air-bladder being near their 
heads 
