540 ON INCREASE IN SIZE AND WEIGHT [pt. iii 



This may mean that growth is accelerated, but a larger number 

 of experiments with more complete statistical treatment will be 

 required to settle the question. 



A word should be said about the possible total reversibility of 

 growth. Regression to the embryonic state was first brought about 

 by Caullery, and recently Davydov has succeeded in reducing the 

 nemertine Lineus lacteus to a state which cannot be distinguished from 

 its blastula. Nothing is known of the chemistry of this process. 



In conclusion it may be said that modern embryology has more 

 and more come to follow the lead of Leonardo da Vinci in subjecting 

 all the aspects of the growth of the embryo to exact measurement. 

 In doing so, it has, as we have already seen, put itself in a position 

 to fuse its studies with those of biochemistry and biophysics. The 

 fruit of this union can only be the understanding of the molecular 

 mechanisms underlying embryonic growth and development, from 

 the egg-cell into the newly hatched animal, whose shape and con- 

 stitution must in the last analysis be regarded as among the properties 

 of what we call matter. 



