VARIATION IN CHILOMONAS UNDER FAVOURABLE AND UNFAVOURABLE CONDITIONS

Abstract

FOB some time past it has seemed to the writer that much of value for the elucidation of the problems of morphogenesis might be gained by quantitative investigations which should give more precise information than we now have of the effects of different environmental conditions on the formative activities of protoplasm. It is, of course, well known that in general the form of an organism is directly influenced by the environment in which it lives. Further the brilliant investigations of such experimental morphologists as Driesch, Herbst, and Morgan, for example, have shown for individual organisms the particular qualitative change which follows a given definite change in the environment. Such investigations can only be regarded as of the highest value and importance, and the field they open up is likely to be one of the most fruitful in biology. Furthermore it seems to me to be a field in which much of fundamental significance may be brought out by the application of the methods of biometry. It is not the place here to enter upon a general discussion of the grounds for this opinion. The time for such a discussion is after a respectable body of objective results have been gleaned by biometric investigations in the field of experimental morphology. It will not, however, be out of place to outline very briefly the nature of some of the problems of morphogenesis which seem especially to need biometric treatment, as in this way the standpoint from which the writer's work in biometry is being done may most easily be made clear. One such problem is this: to what extent and in what manner is the relative constancy of form production capable of modification ? Thus, to take a concrete instance, are " lithium" sea-urchin larvae reared under uniform conditions relatively more or less constant (or, if one pleases, less or more variable) in form than are normal larvae reared under uniform conditions ? Driesch has strongly emphasized that one of the most fundamental problems which biology presents is that, to use his own term, of the " Lokalization morphogenetischer Vorgange." His own work has served the admirable purpose of very sharply and clearly defining the nature of this problem. For its solution, however, he has turned to a teleological principle the " entelechy" of the system. But before taking such a radical step it seems not undesirable to investigate more thoroughly, than has been done the nature and laws of this " Lokalization." After all, how precise is it ? Driesch has frequently cited as one of the most striking of the phenomena which led him to adopt a vitalistic hypothesis, the proportionate division by constriction of the intestine of a sea-urchin larva into three parts. * Of course in the particular case cited of the proportional division of the intestine the practical difficulties in the way of measuring may be insuperable, but this in no way affects the point of principle that in this and riTniinr cases quantitative treatment of the problems of morphogenesis is necessary if real advance is to be made.