48 SCIENCE AND PHILOSOPHY OF THE ORGANISM 



back from elementary organs to elementary processes, the 

 specialisation of the size of those organs may also be said to 

 be the consequence of a typical duration of the elementary 

 morphogenetic process leading to them. 1 



I hardly need to say, that the histology, form, and size 

 of elementary organs are equally an expression of their 

 present or future physiological function. At least they 

 prepare for this function by a specific sort of metabolism 

 which sets in very early. 



The whole sequence of individual morphogenesis has 

 been divided by some embryologists into two different 

 periods ; there is a first period, during which the foundations 

 of the organisation of the " type " are laid down, and a 

 second period, during which the histo-physiological specifica- 

 tions are modelled out (von Baer, Gotte, Eoux). Such a 

 discrimination is certainly justified, if not taken too strictly ; 

 but its practical application would encounter certain 

 difficulties in many larval forms, and also, of course, in 

 all plants. 



Our mention of plants leads us to the last of our 

 analytical results. If an animal germ proceeds in its 

 development from a stage d to the stage g, passing through 

 e and /, we may say that the whole of d has become the 

 whole of/, but we cannot say that there is a certain part of 

 /which is d, we cannot say that /is d + a. But in plants 

 we can : the stage / is indeed equal to a + b + c + d + e + a 

 in vegetable organisms ; all earlier stages are actually visible 

 as parts of the last one. The great embryologist, Carl Ernst 



1 The phrase " ceteris paribus " has to be added of course, as the duration 

 of each single elementary morphogenetic process is liable to vary with the 

 temperature and many other conditions of the medium. 



