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Blood islands are formed in the yolk sac mesodermal area just between the visceral endodermal and ectodermal layers , which supply the red blood cells at the primary stage .
 Blood islands, yolk sac mesodermal area, visceral endodermal, ectodermal layers, red blood cells
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Anatomy 
Text: {0} 
Answer:
 Blood islands, yolk sac mesodermal area, visceral endodermal, ectodermal layers, red blood cells