1907  

"Nature arrives at identical results, in sometimes neighboring species, by entirely different embryogenic processes. . . , The retina of the vertebrate is produced by an expansion of the rudimentary brain of the embryo. ... In the mollusc, on the contrary, the retina is derived from the ectoderm directly. ... If the crystalline lens of a Triton be removed, it is regenerated by the iris. Now the original lens was built out of the ectoderm, while the iris is of mesodermal origin. What is more, in the Salamandra maculata, if the lens be removed and the iris left, the regeneration of the lens takes place at the upper part of the iris ; but if this upper part of the iris itself be taken away, the regeneration takes place in the inner or retinal layer of the remaining region. Thus parts differently situated, differently constituted, meant normally for different functions, are capable of performing the same duties and even of manufacturing, when necessary, the same pieces of the machine."--Creative Evolution (1907) by Henri Bergson