Packard M J, Packard G C, Miller J D, Jones M E, Gutzke W H
J Exp Zool. 1985 Sep;235(3):349-57. doi: 10.1002/jez.1402350306.
Embryos of the agamid lizard Amphibolurus barbatus are at developmental stage 29 of Dufaure and Hubert at the time of oviposition. Mobilization of calcium and other nutrients from the yolk proceeds slowly for the first half of incubation, during which time embryonic growth also proceeds slowly. During the second half of incubation, however, embryos withdraw calcium and other nutrients from the yolk very rapidly, and growth rates are correspondingly high. Approximately 60% of the calcium used by developing embryos is obtained from the yolk, but fully 40% of their requirement is met by calcium mobilized from the eggshell. Very little calcium remains in residual yolk of hatchlings, so this yolk must be used in maintenance metabolism rather than in growth of neonates. No dichotomy exists among oviparous, amniotic vertebrates with respect to sources of calcium used by developing embryos, but one does exist with respect to patterns of mobilization of this element. Whereas calcium is extracted from yolk of embryonic reptiles throughout incubation, it actually is deposited in yolk of embryonic birds after the midpoint in development.
鬃狮蜥（Amphibolurus barbatus）的胚胎在产卵时处于杜福尔和休伯特所定义的发育第29阶段。在孵化的前半段时间里，卵黄中钙和其他营养物质的动员过程缓慢，在此期间胚胎生长也很缓慢。然而，在孵化的后半段，胚胎从卵黄中快速摄取钙和其他营养物质，生长速度相应地加快。发育中的胚胎所使用的钙约60%来自卵黄，但它们所需钙的整整40%是通过从蛋壳中动员的钙来满足的。幼体的残留卵黄中几乎没有钙了，所以这些卵黄必定用于维持新陈代谢，而非用于幼体的生长。在产卵的羊膜脊椎动物中，发育中的胚胎所使用的钙源并无差异，但在这种元素的动员模式方面确实存在差异。在整个孵化过程中，胚胎爬行动物从卵黄中提取钙，而在发育中期之后，钙实际上是沉积在胚胎鸟类的卵黄中。
