Transplantation and Regeneration: Their Bearing on Developmental Mechanics. a Review of the Experiments and Conclusions of the Last Ten Years (1915-1924). By

THIRTY years ago zoologists were mainly occupied with that comparative description of development which had aroused intense interest owing to the overwhelming stimulus of the theory of evolution. The analogy of the developing egg and the developing species from a single undifferentiated cell to a differentiated mass of cells was regarded as an even stronger support to that theory than the direct proof of palaeontology itself. At that time not many realised how far zoologists were becoming committed to far-reaching speculations whose truth it was difficult, if not impossible, to test by actual observation. Owing largely to the genius of a few distinguished men a new science has arisen whose scope it is to analyse by experiment some at least of the actual factors which control the development of the organism, and to build up thereby a new conception of the organism itself. Two outstanding pioneers may be mentioned—WHhelm Roux and Jacques Loeb, both of whom died in 1924.