|Viruses are obligate intracellular parasites which can only be propagated in living cells. Eukaryotic cells can be grown in vitro ('tissue culture') and viruses can be propagated in these cultures, but these techniques are expensive and technically quite demanding. Some viruses, such as influenza virus, will grow in the living tissues of developing embryonated hens eggs.
Egg-adapted strains of influenza virus grow well in eggs and very high virus titres can be obtained. You will be provided with an influenza virus preparation grown in this way.