<P> Among animals which produce one , the yolk ( also known as the vitellus ) is the nutrient - bearing portion of the egg whose primary function is to supply food for the development of the embryo . Some kinds of egg contain no yolk , for example because they are laid in situations where the food supply is sufficient ( such as in the body of the host of a parasitoid ) or because the embryo develops in the parent 's body , which supplies the food , usually through a placenta . Reproductive systems in which the mother 's body supplies the embryo directly are said to be matrotrophic ; those in which the embryo is supplied by yolk are said to be lecithotrophic . In many species , such as all birds , and most reptiles and insects , the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother . In many other animals , especially very small species such as some fishes and invertebrates , the yolk material is not in a special organ , but inside the ovum . </P>
<P> Among animals which produce one , the yolk ( also known as the vitellus ) is the nutrient - bearing portion of the egg whose primary function is to supply food for the development of the embryo . Some kinds of egg contain no yolk , for example because they are laid in situations where the food supply is sufficient ( such as in the body of the host of a parasitoid ) or because the embryo develops in the parent 's body , which supplies the food , usually through a placenta . Reproductive systems in which the mother 's body supplies the embryo directly are said to be matrotrophic ; those in which the embryo is supplied by yolk are said to be lecithotrophic . In many species , such as all birds , and most reptiles and insects , the yolk takes the form of a special storage organ constructed in the reproductive tract of the mother . In many other animals , especially very small species such as some fishes and invertebrates , the yolk material is not in a special organ , but inside the ovum . </P>
this organism is found inside the egg of a chicken
this organism is found inside the egg of a chicken
yolk
yolk