SECTION 3 



ON INCREASE IN COMPLEXITY AND 

 ORGANISATION 



3-1. The Independence of Growth and Differentiation 



The previous section has been concerned solely with the question of 

 increase in size and in mass as the embryo develops; other syn- 

 chronous processes were perforce neglected. These may be compre- 

 hended in one word, differentiation, or increase in complexity and 

 organisation both macroscopic and microscopic. "All generation", 

 said Sir Kenelm Digby, "is made of a fitting, but remote, homogeneall 

 compounded substance; upon which outward Agents, working in 

 the due course of nature, do change it into another substance, quite 

 different from the first, and do make it less homogeneall than the 

 first was. And other circumstances and agents do change this second 

 into a third, that third, into a fourth ; and so onwards, by successive 

 mutations that still make every new thing become lesse homogeneall 

 than the former was, according to the nature of heat, mingling more 

 and more different bodies together, untill that substance be pro- 

 duced, which we consider to be the period of all these mutations." 

 Or, as William Harvey puts it, "For though the Head of the Chicken, 

 and the rest of its Trunck, or corporature (being first of a similar 

 constitution) do resemble a Mucus, or a soft glewey substance: out 

 of which afterwards all the parts are framed in their order; yet by 

 the same operation, and the same Operatour, they are together made 

 and augmented: and as the substance resembUng glew doth grow, so 

 are the parts distinguished. They are Generated, Altered, and 

 Formed at once". Having discussed then in the preceding section 

 the "augmentation" of the embryo, we have now to discuss its 

 "making" or in Harvey's other term, its "framing". 



Framing is undoubtedly not an increase in complexity alone. 

 Woodger has well said, "It is often stated that organisms are just 

 complicated physico-chemical reactions, and it is because they are 

 so complicated that biology has so far made so little progress. But 

 it is evidently not simply a question of complicatedness, because 

 there are plenty of compUcated goings on in the world which no one 



