This beautiful, geometric arrangement of microtubules is about to sort the chromosomes between them into four utterly disfunctional piles, dooming the cells that descend from this egg, which made the disastrous mistake to admit not one but two sperm.

Normally, the egg lacks a centrosome; this is the one truly unique thing that the fertilizing sperm provides to the zygote.  The sperm centrosome duplicates to make the two poles of the zygote’s mitotic apparatus at first cleavage.  Chromosomes duplicate too, in the expectation that each of two daughter cells needs one copy of every chromosome.

When more than one sperm enters the egg, each sperm centrosome duplicates to contribute two spindle poles.  However many centrosomes there are, each one hooks up to chromosomes during mitosis.  Since the chromosomes are only duplicated, then each pair can only distribute copies to two spindle poles.  This means that, in a polyspermic egg, daughter cells inherit random subsets of the genome.  Cells missing whole chromosomes can often divide for a while, and possibly differentiate into some types of tissues, but generally don’t make it very far.  Polyspermic eggs are therefore doomed in most animals.*  

— text by George von Dassow

* In mammals, the early divisions take place without centrosomes at the spindle poles.  The sperm does not apparently provide a functional centrosome.  Does polyspermy in mammals result in the same kind of trouble depicted here?