noun
: a knob of embryonic tissue not divided into germ layers that arises at the primitive knot and contributes to the formation of the posterior part of the vertebrate body
noun
: a knob of embryonic tissue not divided into germ layers that arises at the primitive knot and contributes to the formation of the posterior part of the vertebrate body
Webster's New International English Dictionary. Новый международный словарь английского языка Webster. 2012