为什么VNR一会翻译一会不翻译.好苦恼

为什么VNR一会翻译一会不翻译.好苦恼

that are roughly equivalent in size. In frogs, in which the egg has somewhat more yolk, cleavage proceedsmore rapidly in regions of the embryo having less yolk.In bird eggs the yolk is so massive thatcleavage divisions are restricted to a tiny area of cytoplasm.
不同物种，卵裂方式不同。决定因素主要取决于卵黄的含量。含有少量卵黄的物种（例如哺乳动物），合子分裂得很彻底，子细胞大致平均分裂。蛙卵，卵黄稍微多点，在胚胎的卵黄较少区域发育更快些。鸟卵卵黄很大，卵裂被限制在细胞质很小区域内。