Serpents in general are oviparous; the adder, an exceptional case, is viviparous: for not all viviparous animals are hair-coated, and some fishes also are viviparous.

• 大蛇类通常是卵生的；蝰蛇是一个例外，是胎生的：因为并不是所有胎生动物都是有体毛的，一些鱼也是胎生的。