GENEOLOGICAL. 379 



dung und Formstorung (1880). "To think that 

 heredity will build up organic beings without me- 

 chanical means " is, according to His, " a piece of 

 unscientific mysticism " ; and from many different 

 sides there has been an attempt to analyse the proc- 

 esses of organic growth and embryonic architecture. 

 The task, which is involved in stupendous difficulties, 

 has been touched by the work of O. Hertwig, Pfliiger, 

 Fol, Born, O. Schultze, Berthold, Gerlach, Van Ben- 

 eden, Boveri, Heidenhain, Loeb, Davenport, and 

 many others, but the name of Roux should be par- 

 ticularly associated with the attempt to get nearer 

 some concrete conception of developmental mechan- 

 ism. 



" Developmental mechanics/' he says, " or the causal 

 morphology of organisms, is the doctrine of the causes 

 of organic forms the doctrine of the causes of the 

 origin, maintenance, and involution (degeneration) of 

 these forms. ... In any given case, we must trace 

 back each individual formative process to the special 

 combination of energies by which it is conditioned, or, 

 in other words, to its modi operandi, and each of these 

 modi operandi must be ascertained with respect to 

 place, time, direction, magnitude, and quality. Or, in- 

 versely we may endeavour to determine in the individual 

 structure the special part which is performed by every 

 modus operandi known to participate in the develop- 

 ment of the organism." 



To mention those who have helped Roux towards 

 the realisation of this ambitious aim would be to 

 give a list of the contributors to the ArcJiiv fur Ent- 

 wickelungs-Mechanik. But this could serve no use- 

 ful purpose. 



The problem of development has been passed on 

 to the twentieth century quite unsolved, and we can- 



