The heart of a water-flea can be seen as a transparent sac right above the eggs. It is great fun to see it beating. A nice trick to count the heart beat rate is by tapping a pencil to the pace of the beat. After a minute of counting the taps, you can say how many times per minute the heart beats. 

The triangular muscle (top right) operates the powerful second antennae used for swimming. The gut contents are yellow-brown.

Apart from the unfertilised eggs you can sometimes find winter eggs.