CHAPTER I. 



AN INTRODUCTION TO THE STUDY OF GROWTH. 



Problems Cells Egg-cell Fertilisation Cell-multiplication and 

 cell-enlargement Number of cells in man Nutrition of cells 

 Specialisation Germ layers Methods of growth Cells 

 not simple Theory of development Relations between 

 nucleus and cytoplasm Entire larvae from fractions of the 

 egg Multiple embryos from a single egg Size of animals 

 Growing cells Specialisation antagonistic to regeneration 

 Longevity Rate of growth Onset of decay Two habits of 

 growth Cell-multiplication occurs early Time limitations of 

 development Size in geological time Conditions influencing 

 size Rhythm of growth Summary Outline of succeeding 

 chapters. 



THE living world of which we are a part is ever 

 changing. Unceasingly from seeds and eggs new 

 generations arise, and each day those which have 

 completed the cycle of a life pass to their final disso- 

 lution. The history of these changes forms a record 

 difficult to interpret, yet perennially interesting, since 

 each question solved is at once replaced by the group of 

 problems from which it sprang. Among the current 

 problems I shall select a series, and the study here 

 proposed will deal with those relating to the growth of 

 the brains of animals. To the understanding of them, a 

 review of the more important observations which broadly 

 underlie the laws of growth will form a fitting intro- 

 duction. 



The higher animals possessed of a backbone consti- 



