Packard M J, Packard G C, Gutzke W H
J Exp Biol. 1984 May;110:99-112. doi: 10.1242/jeb.110.1.99.
Total calcium in embryos of an oviparous, colubrid snake (Coluber constrictor L.) rises rapidly during the last half of incubation as the embryos increase in size. Although most of this calcium is drawn from stores in the yolk, hatchlings contain more calcium than was present in yolk of eggs at oviposition. Because shells from eggs incubated to hatching contain less calcium than do shells from freshly-laid eggs, the extra calcium appears to be drawn from the eggshell. Indeed, approximately 20% of the calcium required for development in this snake is obtained from the eggshell, with the remainder coming from the yolk. Thus, embryos of oviparous snakes, like embryonic chelonians, crocodilians and birds, withdraw calcium from their eggshells and do not rely exclusively on calcium supplied in their yolk for support of growth and development.
卵生游蛇科蛇类（王蛇）胚胎中的总钙含量在孵化后半期随着胚胎的生长而迅速增加。虽然这些钙大部分来自卵黄中的储存，但幼体所含的钙比产卵时卵黄中的钙更多。由于孵化至幼体孵出的卵的蛋壳所含钙比刚产下的卵的蛋壳少，额外的钙似乎是从蛋壳中获取的。实际上，这种蛇发育所需的钙约20%来自蛋壳，其余来自卵黄。因此，卵生蛇类的胚胎，如同龟鳖类、鳄类和鸟类的胚胎一样，会从它们的蛋壳中摄取钙，并非仅仅依赖卵黄中提供的钙来支持生长和发育。
