158 BIOLOGICAL LECTURES. 



of these two courses ; hence an ontogenetic and a phylogenetic 

 developmental mechanics are to be perfected. 



Since the object of the developmental mechanics of ontogeny 

 is the investigation of phenomena which are hurried through 

 rapidly in present time, it will, of course, yield greater results 

 than phylogenetic developmental mechanics, the phenomena of 

 which belong in great measure to the past, and, so far as they 

 occur at present, must be carried on with extreme slowness. 

 But in consequence of the intimate causal connections existing 

 between the two, many of the conclusions drawn from the in- 

 vestigation of ontogeny will also throw light on phylogenetic 

 processes ; moreover, phylogeny, even within the limits of its 

 present occurrence, is not entirely inaccessible to investiga- 

 tion ; many a causal connection may be ascertained by means 

 of experiment, as has already been shown in the case of artifi- 

 cial selection. 



The components with which the doctrine of phylogenesis has 

 hitherto exclusively dealt, viz., variation (adaptation) and 

 heredity, are still more complicated than the above-mentioned 

 complex components. Nevertheless, this distinction at the 

 same time represents the reduction of extremely diverse phe- 

 nomena to two, albeit in their special modi operandi exceed- 

 ingly variable, and hence not " constant " or " uniform," com- 

 ponents. The word "variation" is to a much greater. degree 

 even than the word "heredity" a collective term for results 

 which are in a certain sense uniform, but which may depend 

 on very diverse modi operandi. Hence developmental mechan- 

 ics has before it the further task of searching out, first, the 

 various constant sub-components of the effects so named, and, 

 second, the causes of these effects. 



In this direction, too, encouraging attempts have been made. 

 While Darwin's doctrine of natural selection represents only 

 collective causes (Aufspeicherungsursachen) of given characters 

 on the basis of the survival, non-extermination, of the 

 fittest, the new doctrine of mechanomorphoses of Julius v. Sachs 

 (8) is already giving us an insight into actually operant, and 

 hence immediate formative causes, into the formative modi 

 operandi of the prehistoric life of organisms. 



