3 There are other trends in the attempt to meld evolution and development which immodesty permits me to add. I have been concerned over the years with the selection forces which might have produced larger organisms and therefore a development of increasing complexity. This is nowhere more evident than in the multiple evolutionary origins of multicellularity and all the variety of developmental mechanics that have gone with it. (I discuss this and related themes in various places, but see especially The Evolution of Development (1958; (1)) and Size and Cycle (1965; (2)). To some degree these examples of the bringing together of evolu tion and development are exceptions. By far the most important historical trends in this century have been the success of in dividual disciplines. Embryology had its great flowering be ginning in the last century, coming to a climax with the work of Spemann on induction in the first two decades of this cen tury. Genetics has had an extraordinary continuing series of revolutions beginning with the rediscovery of Mendel and pro gressing through Morgan to the flash flood of molecular genetics and the structure of DNA. This flood was a flash only in the sense that it rushed upon us with amazing speed; its effects in the form of important and exciting work produced has not subsided and we are still in a peak period of molecular genetics.
