1. Membranous structure that functions as the circulatory system in mammalian embryos until the heart becomes functional
   - yolk sac, vitelline sac, umbilical vesicle

Type of: sac

• Meloidae
• Melolontha
• Melolontha melolontha
• melolonthid beetle
• Melolonthidae
• melon
• melon ball
• melon tree
• melon vine
• Melophagus
• Melophagus Ovinus
• Melopsittacus
• Melopsittacus undulatus
• melosa
• Melospiza
• Melospiza georgiana
• Melospiza melodia
• melphalan
• Melpomene
• melt
• melt off
• meltable
• meltdown
• melted
• melter