1. A child is brought to the pediatrician because of perianal itching, which has been disturbing the child's sleep. Physical examination reveals scaly skin in the perianal region. The physician instructs the parents to place transparent tape on the perianal region the next morning, and then retur n to the office. In the office, the tape is transferred to a microscope slide, and low-power examination of the tape reveals oval eggs that are flattened along one side. The microorganism most likely responsible for the child's symptoms is