INTRODUCTION 



In the preceding discussion of the nature of the genetic material we 

 had to touch many times upon the action of this material, since many 

 of the inferences concerning the nature of the genetic material are 

 derived from an analysis of action. We have mentioned a number of 

 facts and interpretations which, however, were not discussed in de- 

 tail, such a discussion being reserved for the present chapter. When 

 speaking of the action of the genetic material it is at once realized 

 that in some way practically all of biology falls into this chapter. In 

 the last analysis, all morphological, physiological, and psychological 

 features of organisms are genetically controlled, directly or through 

 a reaction norm. As a consequence, evolution may also be considered 

 dependent on genetically controlled processes. In view of this, the 

 impossibility of an exhaustive analysis of all genie action is apparent. 

 It appears to be the task of genetical theory to unravel the generalized 

 laws and concepts that cover all possible types of genie actions in such 

 a way as to make them generally intelligible, whatever the additional 

 details may be if a specific case is to be analyzed; further, to lay 

 emphasis on genie actions which might throw light, in turn, upon the 

 nature of the genetic material. Though all morphology and physiology, 

 embryology, and especially experimental embryology should con- 

 tribute to such an analysis, most insight will be expected from a study 

 of the facts of organization as accomplished by the processes of de- 

 velopment with different genetic basis. Such a study has been called 

 "physiological genetics," meaning by the term "physiological" the 

 functional aspect, that is, genie action or dynamic genetics as opposed 

 to static or statistical genetics. (This term was brought to the fore, if 

 not actually introduced, when I surveyed the field analytically in my 

 Physiological Theory of Heredity, 1927.) When the emphasis is upon 

 the developmental features of the genetically diflFerent phenotypes, the 

 term "phenogenetics" (Haecker, 1918) is frequently used. In any case 

 physiological genetics and phenogenetics have a broad line of con- 

 tact with experimental embryology, since many of the facts brought to 

 light by the latter are relevant for genetics. 



Experimental embrj'ology, however, keeps aloof (and rightly so) 

 from such parts of the common field which are predominantly genetic 

 (e.g., dosage problems). It is rather strange that some embryologists 

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