Up to 1 million eggs are released when the strobila of an adult T. crassus leaves the intestine of northern pike and enters freshwater. The egg has a thin membrane, since desiccation is not a problem in the aquatic environment. This egg is unembryonated, but it will embryonate and hatch within a few days, releasing a coracidium. When ready to hatch, an operculum at the tapered end of the egg (not visible yet) will open, enabling the coracidium to escape.