EXPERIMENTAL MORPHOGENESIS 93 



called by Roux " correlation of masses," though this author 

 originally intended to express by this term only some sorts 

 of passive pressure and deformation amongst embryonic 

 parts as discovered especially by His. 



We must be cautious in admitting that any organic 

 feature has been explained, even in the most general way, 

 by the action of physical forces. What at first seems to be 

 the result of mechanical pressure may afterwards be found 

 to be an active process of growth, and what at first seems 

 to be a full effect of capillarity among homogeneous elements 

 may afterwards be shown to depend on specialised metabolic 

 conditions of the surfaces as its principal cause. 1 



There are other physical phenomena too, which assist 

 morphogenesis ; osmotic pressure for instance, which is also 

 well known to operate in many purely physiological processes. 

 But all these processes are only means of the organism, and 

 can never do more than furnish the general type of events. 

 They do not constitute life ; they are used by life ; let it 

 remain an open question, for the present, how the phenomenon 

 of " life " is to be regarded in general. 2 



On Growth. Among the internal morphogenetical means 

 which are of a so-called physiological character, that is, 

 which nobody claims to understand physically at present, 



1 According to Zur Strassen's results the early embryology of Asmris 

 proceeds almost exclusively by cellular surface-changes : the most typical 

 morphogenetic processes are carried out by the aid of this "means." As a 

 whole, the embryology of Ascaris stands quite apart and presents a great 

 number of unsolved problems ; unfortunately, the germ of this form has not 

 been accessible to experiment hitherto. 



2 Rhumbler has recently published a general survey of all attempts to 

 "explain" life, and morphogenesis in particular, in a physico-chemical way 

 ("Aus dem Liickengebiet zwischen organismischer und anorganismischer 

 Natur," Ergeb. Anat. u. Entw.-gesch. 15, 1906). This very pessimistic survey 

 is the more valuable as it is written by a convinced " mechanist." 



