DEVELOPMENTAL MECHANICS. 151 



Accepting this latter term, the task of developmental me- 

 chanics would be the reduction of the formative processes of 

 development to the natural laws which underlie them. 



It is, however, preferable, at least in those cases to which 

 the expression constant mode of operating is more applicable, 

 to employ this phrase instead of the term natural law, which 

 is based upon anthropomorphic conceptions of nature. It be- 

 hooves us, especially when entering on a new and extensive 

 field of investigation, beset with quite special difficulties, to 

 call the thing to be sought by its own name, instead of employ- 

 ing an expression which is foreign to its nature. 



Since, moreover, all the modi operandi underlying causality, 

 and hence all modi operandi which may become the subject of 

 our investigation, are " constant or uniform," this adjective 

 may generally be omitted, and it is sufficient to say simply 

 modi operandi, instead of natural laws. Instead of the " law" of 

 the refraction of light we may also speak of the modus operandi 

 of refraction; instead of the "laws" of functional adaptation 

 let us say the modi operandi of functional adaptation, e.g., of 

 the muscles. This designation at the same time renders 

 impossible in Biology one widespread, incorrect usage of the 

 term "law," viz., the use of the term to designate facts or 

 results instead of operations, as, for instance, in the current ex- 

 pression "Bell's law." When we attempt to use, instead, 

 Bell's modus operandi, it becomes at once apparent that this 

 term is inapplicable to the "fact" of the motor nature of the 

 anterior, and the (supposed) purely sensory nature of the pos- 

 terior nerve-roots. 



If, furthermore, we define the general task of developmental 

 mechanics so that it shall include the fewest mysterious con- 

 cepts, and hence in a way which is simplest and most compati- 

 ble with the immediate method of procedure, we must reduce 

 the processes of organic formation to the fewest and simplest 

 modi operandi. This, of course, implies that for each of these 

 modes the simplest expression is to be sought. 



All operating, and hence also its product, all operation, has at 

 least two causes or components, since in last analysis nothing 

 can change its condition of itself. 



