By SYDNEY SMITH
Department of Zoology, Cambridge
Effective teaching requires effective communication. Before the communication can begin, observation, selection and codification into mutually acceptable terms between teacher and taught have all to take place. The codes by which the supposed essential nature of the material is defined, become more refined and more circumscribed in the give and take between teacher and taught, until--in the ideal situation--the distinction between the two breaks down and both become involved in the amplication of information by direct reference to the material to hand as well as increase in the elegance and comprehensive economy of the codes through which information concerning embryos is transmitted. It is clear that the act of codification is one of model building, and, whether this is conscious or not on the part of the teacher, such preliminary formulation is absolutely unavoidable in embryological teaching; accordingly some examination of formerly used models and of the currently fashionable ones is perhaps not out of place in the context of this symposium.
To teach embryology at all some degree of self-confidence has to be developed by the teacher. This can be achieved only by study of the living embryo, and, in our modern fashion, study means experimental observation. But embryology is at one and the same time the embodiment of both progress and the most reactionary conservatism, so that the morphological study of fixed and serially sectioned embryonic stages has still to form the basis for class instruction. The impatient, but premature, rejection of morphology as outmoded has not always proved helpful for the progress of our experiments, and the purpose of this essay in interpretation is to stimulate a co-operative tolerance between our experimental and morphological urges.
Embryos are notoriously difficult subjects for study: in occurrence they are, for the most part, severely limited in time; they are frequently hidden away and are thus relatively inaccessible; the development of a select few blatant and prolific breeders tends to become trite, because over-familiar, and it is an occupational liability in the embryologist to be subject to irrational moods of violent and over-confident extrapolation from the few known to the un numbered unknown. The urge to extrapolate is very natural, for all living things have some sort of embryonic development during which the massively stable though dynamically maintained complexes latent in the structure of the germ become, through a dynamic, ordered and reproducible sequence of