36 Heredity. 



latter. The developing impulse which in the one ca^e 

 is transferred from the ancestral species to the entire 

 group of species, and in the other case from the ances- 

 tral cell to the entire group of cells, assumes in both 

 cases the same form of a branching wave-motion. Any 

 one who accepts the fundamental law of development 

 will find it only natural that the microcosm of the onto- 

 genetic f cell-tree' should be a diminution, and to some 

 degree distorted reflection of the phylogenetic ' species- 

 tree. ' 



"As we can only explain and render intelligible a 

 complicated and obscure phenomenon b}^ dividing it into 

 its separate elements, and by the exact analysis of these 

 parts, so it is necessary to penetrate to the ultimate 

 elementary facts of our mechanical theory of develop- 

 ment. 



" Now the biogenetic process as a whole is the highly 

 compound resultant of the developmental history of all 

 species of organisms. These consist again of the life 

 histories of the individuals, just as the latter are again 

 made up of that of the constituent plastids. 



" The development of each plastid, however, is in its 

 turn only the product of the active movements of its 

 constituent plastidules. Now we have seen that the de- 

 velopmental impulse of the. branches and classes, the 

 orders and families, the genera and species, the individ- 

 uals and plastids, always and everywhere has for its fun- 

 dimental characteristics the branched wave-motion. Ac- 

 cordingly the molecular plastidule-motion, which lies at 

 the bottom of all the phenomena of life, can have no 

 other form. We must conclude that this ultimate cause 

 of all the phenomena of life, that the invisible activity 

 of the organic molecules is a branched wave-motion. 

 This true and ultimate causa efficiens of the biogenetic 



