Get the Popular Science daily newsletter💡 Breakthroughs, discoveries, and DIY tips sent six days a week. Eggs are pretty incredible. They must be sturdy enough to keep the precious cargo inside safe, yet soft enough for a baby bird, crab, or snake to push through when the time is right.  Over millions of years, some egg laying species have evolved a wide variety of shapes, sizes, colors, and methods for laying them to ensure the survival of the next generation. Here, we break down three of nature’s most interesting egg laying strategies, from spongy blue crab eggs, gelatinous salamander eggs, and more.  An assortment of eggs from the collection at the National Museum of Natural History. The large egg in the middle is an ostrich egg. Image: Christina Gebhard, Smithsonian. Blue crabs and their amazing ‘sponges’ Blue crabs (Callinectes sapidus) go through a complex series of life stages. As larvae they live in coastal waters off the mouth of an estuary settling into the sea grasses in the brackish water near the Atlantic Ocean. As …