Hans Freeman and Hilde mangled were pioneers of developmental biology they showed how the pattern of the embryo is created by interactions between one group of cells and another in 1924 they made a famous discovery they found that a small piece of tissue called the organizer taken from a specific site in the early frog embryo and transplanted to another embryo could control the behavior of neighboring cells and direct the formation of an entire body axis the key experiment is reenacted here by a modern developmental biologist using the Frog Xenopus laevis to Xenakis embryos are maneuvered under the dissecting microscope the embryos are beginning to ghast relate the blastopore where cells are tucking into the interior is visible as a dark crescent in the embryo on the left the dorsal lip of the blastopore contains the organizer cells with a pair of forceps and a fine tungsten needle a block of organizer tissue is cut from the embryo on the left using a hair plucked from a human eyebrow the block of tissue is gently pushed into a site on the ventral side of the other embryo an hour later the graft has healed into the host embryo and the organizer cells have been integrated at an ectopic site two days later the host embryo has developed into conjoined twins the grafted organizer has caused the host cells around the graft to form a second body axis complete with central nervous system eyes so mites and other structures you