122 INDIVIDUALITY IN ORGANISMS 



far as nutritive or other conditions permit, and then 

 ceases. There can be Uttle doubt that relations of 

 dominance and subordination exist during embryonic 

 stages, and that these are factors in determining what 

 occurs in later stages. According to this view, the 

 difference between these eggs and those in which a high 

 degree of embryonic reconstitution occurs is primarily 

 a difference in the stability or fixity of the effects of 

 previously established metabolic gradients. At the one 

 extreme are eggs in which axial differences at the be- 

 ginning of embryonic development are probably largely 

 or wholly differences in metabolic rate, at the other, 

 those in which specialization and differentiation of parts 

 have gone far beyond this condition. The egg, in short, 

 is an individual, and some eggs are more highly special- 

 ized individuals than others. 



The proportional relations of parts in reconstitution, 

 of which much has been made by Driesch, Morgan, and 

 others, are obviously, so far as they exist, dependent 

 upon metabolic relations between the parts. On a short 

 piece of Planaria, for example, a smaller head usually 

 develops than on a long piece. This fact has often been 

 regarded as in some way associated with the fact that 

 the shorter piece will produce a smaller animal than the 

 longer and that the size of the new head foreshadows 

 the size of the animal. As a matter of fact, the size 

 of the head formed by pieces of the same size may 

 differ widely in different cases and can be controlled 

 experimentally to a very large extent by controUing 

 metabolic conditions. The higher the metabolic rate in 

 the region x, Fig. 58, in relation to that of the region y, 

 the larger the head, and vice versa. The size of tJie 



