The main reason I enjoy working at the microscope is that I never know exactly what I will see.  Today while counting a preserved phytoplankton sample collected at the Rhode Island shelf break I spotted these cells:

This is a chain of diatom cells (genus: Detonula, I think) undergoing a life cycle stage that allows them to get bigger.  Diatom cells get smaller every time they divide.  At some point, the cells are too small to divide anymore and must form either sexual stages or auxospores to get big again.  In this photo the top cell in the chain is relatively small and does not appear to be vegetative (i.e. able to divide).  The second cell down the chain has a small top half and a much larger bottom half.  This cell formed an auxospore.  The third and forth cells down the chain are large and contain cytoplasm and chlorophyll (the yellow pigment).  These cells are probably the daughter (and grand-daughter) cells of that auxospore.  Because the cells are in a chain, it is possible to see the history of this life cycle response.

I found a very similar image of Detonula auxospores here.