| 单词 | yolk sac |
| 释义 | yolk sac in British Englishnoun zoology 1. the membranous sac that is attached to the ventral surface of the embryos of birds, reptiles, and some fishes and contains yolk 2. the corresponding part in the embryo of mammals, which contains no yolk yolk sac in American English Zoology 1. a saclike vascular membrane containing yolk, an outgrowth from the ventral surface of very yolky vertebrate embryos, as those of fishes, birds, or reptiles, that supplies nourishment to the embryo 2. a homologous organ in most mammalian embryos that contains no yolk and that becomes a vestige at an early embryonic stage |
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