There are more than 5000 species of single-celled eukaryotes in the biological phylum known as the Apicomplexa, including the parasites responsible for malaria, neurological birth defects, and opportunistic infections associated with HIV/AIDS. These ancient protozoa provide a unique window into the evolution of subcellular organelles that have long fascinated cell biologists. Familiar features help to elucidate the origins, functions and design parameters for the secretory pathway,...