Review of course organization. Life on earth has a long history, measured in billions of years. The oldest forms of life we know about are the stromatolite-forming bacteria. The present diversity of life on earth is a result of a process of evolution. The somewhat surprising feature that unites all animals and differentiates all of them from other organisms is an early stage of embryonic development called the blastula.
All animals pass through a blastula stage.
No members of any other kingdom form a blastula. Animals, fungi, plants, and protists are all eukaryotes. To a person uninstructed in natural history, his country or seaside stroll is a walk through a gallery filled with wonderful works of art, nine-tenths of which have their faces turned to the wall. 8-9 provides a clear, brief description of the 6 kingdoms. See Figure 1.7 for representatives of each kingdom.