82 THE RATE OF GROWTH [ch. 



Aristotle its Form was the essence, the archetype, the very "nature" 

 of a thing, and Matter and Form were an inseparable duahty. 

 Even now, when we divide our science into Physiology and Mor- 

 phology, we are harking back to the old Aristotehan antithesis. 



To sum up, we may lay down the following general statements. 

 The form of organisms is a phenomenon to be referred in part to 

 the direct action of molecular forces, in larger part to a more complex 

 and slower process, indirectly resulting from chemical, osmotic and 

 other forces, by which material is introduced into the organism 

 and transferred from one part of it to another. It is this latter 

 complex phenomenon which we usually speak of as "growth." 



Every growing organism; and every part of such a growing 

 organism, has its own specific rate of growth, referred to this or 

 that particular direction ; and it is by the ratio between these rates 

 in different directions that we must account for the external forms 

 oiall save certain very minute organisms. This ratio may sometimes 

 be of a simple kind, as when it results in the mathematically 

 definable outhne of a shell, or the smooth curve of the margin of a 

 leaf. It may sometimes be a very constant ratio, in which case the 

 organism while growing in bulk suffers httle or no perceptible change 

 in form; but such constancy seldom endures beyond a season, and 

 when the ratios tend to alter, then we have the phenomenon of 

 morphological ''development,'' or steady and persistent alteration of 

 form. 



This elementary concept of Form, as determined by varying rates 

 of Growth, was clearly apprehended by the mathematical mind of 

 Haller — who had learned his mathematics of the great John 

 Bemoulh, as the latter in turn had learned his physiology from the 

 writings of Borelh* It was this very point, the apparently un- 

 limited extent to which, in the development of the chick, inequalities 

 of growth could and did produce changes of form and changes of 

 anatomical structure, that led Haller to surmise that the process 

 was actually without Hmits, and that all development was but an 

 unfolding or "evolutio," in which no part came into being which 



* "Qua in re Incomparabilis Viri Joh. Alph. Borelli vestigiis insistemus." 

 Joh. Bernoulli, De motu musculorum, 1694. 



