LIFE-PHENOMENA. 155 



tinuous division of the fertilized egg-cell, are exactly alike, 

 and cannot be distinguished from each other. But gra- 

 dually a division of labour occurs among them by their 

 assuming different offices. Some accomplish nutrition, others 

 reproduction, others protection, others locomotion, and so 

 on. We may translate this into the language of the theory 

 of the tissues and say : some of these cells become intestinal 

 cells, others muscle-cells, others, again, bone-cells, nerve-cells, 

 cells of the sense-organs, of the reproductive organs, etc. 

 Thus we see that the whole course of the evolution of the 

 individual corresponds in its essential features to that pre- 

 supposed course of phylogenetic development, and thus 

 affords a striking confirmation of our fundamental law of 

 Biogeny. 



This observation naturally leads to a brief examination 

 of the physiological functions, or vital activities, which are 

 concerned in the evolution of the individual as in that of 

 the race. At first sight a great number of complex pro- 

 cesses seem to blend and co-operate here ; all of these can, 

 however, in reality be reduced to a few simple organic 

 functions. These vital activities are : (1) Growth ; (2) 

 Nutrition ; (3) Adaptation ; (4) Reproduction ; (5) Heredity ; 

 (6) Division of Labour, or Specialization ; (7) Atavism ; 

 (8) Coalescence. Heredity, Adaptation, and Growth are of 

 especial importance in the evolution of the organic body ; 

 these must, therefore, be regarded as especially formative 

 functions. 



Of all vital phenomena, growth may be regarded as the 

 one which plays the chief part in the evolution of the 

 individual organism, and as the really fundamental function 

 of evolution. The bearing of this function on the evolu- 



