It depends on the species. For instance, most mice will start out as a tube, and then they turn inside out at embryonic day 8 (I think, It may be earlier though

It depends on the species. For instance, most mice will start out as a tube, and then they turn inside out at embryonic day 8 (I think, It may be earlier though). Whereas rats, dogs, and humans do not do this. And that's just the mammalian development that has been under a lot of study. What other vertebrates do, well, that takes a bit more funding!