similar character have been made by Jennings on variation in Paramecium[1]. The first necessity in all such analytical studies must be a precise description and definition of the things which are to be analyzed. Such a description the application of biometric methods furnishes.
In what has been said regarding biometry as a method of group description reference has been made, for the sake of simplicity of illustration, to groups of « individual organisms ». The same considerations, however, apply with equal or perhaps even greater force to the study by biometrical methods of groups of « like » parts or organs within the single individual. Appropriate quantitative methods make it possible to detect and analyze the most subtle phenomena of differentiation in the development and growth of the individual. In the absence of methods for dealing with a group of parts or individuals as such one would be quite unable to attack a whole series of interesting and fundamental problems of morphogenesis. Such problems, for example, as the precision of morphogenetic localization, or the degree of variability of successively regenerated structures (does the morphogenetic mechanism «learn» to work better with practice ?), or the existence and nature of fundamental laws of growth determining the general features of the tectonics of large groups of plants and animals, etc. There is a host of problems of morphogenesis of this general character as yet hardly touched at all by the biologist. Biometric methods which enable us to deal with groups of things or events as groups furnish the key to the successful attack on these problems. Pioneer work in this direction is being done[2] but there is a vast and fertile field here, the proper cultivation of which will demand the combined efforts of many workers. To the application of appropriate biometric methods in this field we may confidently look, I think, as the source of a significant advance in the building up of a causal morphology.
The second fundamental contribution of biometry to
biology lies in the fact that it has shown, and in the future
