VARIATION IN CHILOMONAS UNDER FAVOURABLE 
AND UNFAVOURABLE CONDITIONS. 
By RAYMOND PEARL. 
For 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 proto- 
plasm. 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 morpho- 
genesis 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. 
