Ostium: insects circulatory system

I will alter this answer in response to the poster's comments.

Looking at: https://genent.cals.ncsu.edu/bug-bytes/circulatory-system/

The diagram doesn't show the digestive system - so no anus.

I see that there is expected to be an ostium (hole) near the end of the heart. Think about where in the heart the many valves are located, then look at the segments of the abdomen and work out what happens with the heart when the abdomen extends or contracts, which you can see in bees.

What is more interesting in all the diagrams is the decision about whether the heart pumps just to the head, or also through pipes to the ventral region.