Croonian Lecture :—Organizers in animal development

One of the most remarkable features of the phenomena of life is their uniformity in the most unlike living forms. This fact enables us to choose for our researches such forms as will be, for one reason or another, the most suitable for observation or experiment. The results thus reached must, however, by no means be generalized without further proof; but again and again observations made on favourable subjects have been confirmed by further study in less favourable ones. The fertilization of the egg, for instance, was observed first in the eggs of the sea-urchin, that is, in a species as unlike as possible to any higher animal; yet it has been shown since that fertilization goes on in the same way in all animals. The beginnings of a human individual do not differ essentially from those of an echinoderm. I hardly suppose that many of you have up to the present taken any particular interest in the early development of the common newt, my only subject of research for the greater part of my life; I hardly think it is to such interest that I owe the honour of delivering this lecture. I imagine it was rather the conviction that the laws of development established for this low vertebrate hold true for all vertebrates, nay, for all animals; that development even of man follows the same principles. But for the same reason I dare not presume that all of you have present in your mind the first steps of development of the newt’s egg. It will, therefore, be my first task to recall them to your memory.