Fig. 2

Transplantation of a piece of ectoderm containing a portion of the dorsal lip of the blastopore from lightly pigmented embryo a to darkly pigmented embryo b results in a second neural plate (c). The result is a double embryo, i.e., conjoined twins (d, e). This shows that any portion of the ectoderm is capable of producing a neural plate and subsequent development. In an ordinary, single embryo the dorsal (top) part of the ectoderm produces the brain and spinal cord, while the lower (ventral) hemisphere produces the epidermis, which becomes skin. This sketch, which depicts the original experiments by Hilde Mangold and Hans Spemann [30], is by Victor Twitty. From [182] with permission from Macmillan Education