Organizers in Development and the Organizer Concept

Abstract

A critical survey of a great vol. of exptl. investigation and an attempt to attain an organizer concept based on development in general, not merely on amphibian development. It is pointed out that the so-called primary organizer of amphibians is not primary, does not determine axiate pattern in natural development, is not absolutely necessary for neural differentiation, and has not been proved to be specific in action. The primary amphibian organizer determines axiate pattern before development begins, probably in the ovarian oocyte. In general an organizer is a determiner or inductor of a spatial pattern. Organizers or reorganizers of axiate pattern have been shown in many cases to be purely quantitative extraorganismic differentials which influence rate of metabolism. The exptl. evidence, as opposed to opinion, indicates that axiate patterns in their beginnings and simplest forms consist in graded quantitative differentials in general metabolism, associated with enzyme and other differentials in the protoplasms concerned. It also indicates that organizers and reorganizers of axiate pattern are primarily determiners or inductors of gradient patterns. Whether, or to what extent, they do more than this remains to be detd. Inductors of particular organ systems or organs, such as the amphibian lens, balancer, otic vesicle, etc., are probably not actually organizers, but merely inductors. The specificity of effect in these cases apparently depends on the reacting system. It is still open to question whether these inductors or some of them are primarily anything more than local activators.