Hydrozoan eggs can only be fertilized at the site of polar body formation.
D000818:Animals; D005260:Female; D005306:Fertilization; D006829:Hydra / Q000502:physiology*; D008297:Male; D010063:Ovum / Q000648:ultrastructure; D010781:Photography; D013084:Sperm-Ovum Interactions; D015053:Zygote / Q000648:ultrastructure