28o C. M. Child. 



differ from anything in the germ-cell. When, however, we con- 

 sider the matter from the physiological side wt can trace a certain 

 relation between the cell and the fully formed organism; both 

 exhibit characteristic functional activities and frequently we 

 can trace a given functional complex from the cell through on- 

 togeny by its effect upon organization. This, I think, is the real 

 significance of His' "organbildende Keimbezirke" and Wilson's 

 ('04) formative substances in the egg-cytoplasm. But the 

 designation of these regions as formative regions or substances is 

 a morphological mode of expression which seems to me misleading. 

 All living complexes are formative, or may be under proper condi- 

 tions; but they are formative because they are functional. Let us 

 consider briefly a case in point, viz: the typical form of the pos- 

 terior end in Leptoplana or Stenostoma. This is a characteristic 

 of the species, yet I have shown that it depends largely upon 

 mechanical conditions of tension for its formation. The tension 

 is the result of typical activity on tissues of a typical physical 

 quality in a typical environment. The typical activity depends 

 again on a typical constitution, and so on. What is transmitted 

 from the previous generation? Certainly not tail-germs, nor tail- 

 forming substances, nor anything that is directly related to the 

 tail of the adult. In this case the "tail" is primarily a physical 

 arrangement of material resulting from a characteristic complex 

 of physical and other conditions. In other cases the analysis 

 may proceed on widely different lines but the result must be 

 similar. 



I believe it can be shown that morphological conceptions of 

 development are all anthropomorphic in character and related to 

 our conceptions of man-made structures composed by adding 

 element to element. It becomes more and more evident as our 

 knowledge increases that these conceptions must be discarded. 

 But we cannot as yet substitute for them any adequate conception; 

 we can compare life to nothing but itself. It is perfectly evident 

 that with the physics and chemistry of the past and present we can 

 never hope to interpret the phenomena of life, but we are 

 entering on a period which promises that our physical and 

 chemical conceptions will be as profoundly transformed by 

 increasing knowledge of the processes of living organisms as our 

 conceptions of life ever were by the adoption of physico-chemical 

 hypotheses. 



