Embryo of Physa marmorata (Pond snail) inside the egg three days after laying. The embryo of pulmonata gastropods shows a characteristic rotational behaviour, explained as the necessity to stir the gas/fluid microenvironment inside the egg capsule. The rotation is propelled by ciliar activity and is boosted by low levels of oxygen. (100X magnification).

A ready to hatch egg capsule containing a adult-shaped pond snail (Physa marmorata). The heart pulsation activity is clearly visible. (40X magnification )

Physa marmorata