And they reproduce when the winter rains produce big ponds of water. I may be splitting a point here, but I think it's only fair acknowledging the fact that thisdid not really enable vertebrates to invade land. The suggestion is that this egg is sealed off from thesurrounding environment. And that is absolutely not true either. Not only is there an exchange of oxygen and carbon dioxide between the embryo and theenvironment, but there is also the exchange of water.
Bird eggs lose water.
Bird eggs need to loseabout 15 percent of their initial weight in the form of water or the embryo isn't going to hatch. So that's not a cleidoic egg if it has to lose water. And reptile eggs must take up water. Reptile eggs have to soak up water from the soil in which they are buried in order to successfullydevelop. If they don't, they won't hatch.