282 BIOLOGICAL LECTURES, 



extent of complexity in the germ as compared with the com- 

 plexity of the fully developed organism. 



He who finds little difficulty in passing from the simple to 

 the complex, from the homogeneous to the heterogeneous, will 

 take an epigenetic view of development. The physiologist, who 

 deals with processes, who is ever mindful of the Heraclitean 

 flux, inclines naturally to this view. On the other hand, he 

 who readily idealizes and schematizes, whose mind is endowed 

 with a certain artistic keenness, an appetite for forms and 

 structures, and a tendency to make these forms final patterns, 

 eternal molds, more permanent than the substance that is 

 poured into them such a one will find more difficulty in 

 understanding how the homogeneous can become the hetero- 

 geneous. Of this type is the modern morphologist who is con- 

 tinually diagrammatizing, who has his eye fixed on complex 

 static structures and conceives the continually changing form 

 of the developing egg as a series of kinematograph pictures in 

 three dimensions of space. He is as much inclined to Plato- 

 nize as is the modern physiologist to reason along lines sug- 

 gested by Aristotle. He is by nature a preformationist. 



Just as Wolff's followers have split into two schools one 

 believing in little, the other in much preformation in the germ 

 so Darwin's followers have split into two schools, the Neo- 

 Lamarckians and the Neo-Darwinians, in obedience to the two 

 psychological tendencies to which I have called your attention. 

 The Neo-Darwinians, in laying great stress on the segregation, 

 stable and complex intrinsic structure of the germ plasma 

 and its importance as a vehicle of hereditary characters, and in 

 attributing less value to the extrinsic factors, like food and 

 environment, are allying themselves with theorists of the 

 type of Parmenides and Plato. On the other hand, the Neo- 

 Lamarckians who believe in the permanent change-producing 

 effects of the extrinsic factors (environment, etc.) on structure, 

 and attribute less value to the architecture of an intrinsic vehi- 

 cle of heredity (germ plasma), range themselves with Heraclitus 

 and Aristotle. 



The amount of differentiation displayed during the ontogeny 

 of an organism or during its phylogenetic history will be 



