Hydraulics

Under the surface—
Teeming channels and stations
Subterranean, subcutaneous

Liquids moving in
confined spaces, under pressure
transmitting equally in all directions  

Our hearts have four chambers—
Seastars have no heart at all
Octopi have three and copper blood

Zebrafish can mend
their broken hearts in two months
The wood frog shuts down its heart in winter