How are rods and cones similar?

In the human eye, cones look like a cone, while rods look like short rods. Rods are connected in "parallel", and they detect minimal amounts of light. Cones tend towards a "serial" transmission to the nervous system. Cones also come in various types -- red detecting, green detecting, or blue detecting -- so they enable color vision. Books have been written on this subject, and I wrote a short paragraph.