DEVELOPMENT 215 



materials from the physical environment, or from reserves in the 

 egg, or from the blood-stream of the parent, and it assimilates 

 these materials into itself as the substance of new nucleo-protein 

 and cytoplasmic materials. But as these new cells are formed 

 they are assembled, by definite, specific cell-division planes and 

 rates of cell- divisions into specific cell-configurations so that 

 organ-anlagen, and later on, tissue-configurations, are established. 

 It is this assembling, building, or tectonic activity that is the one 

 to which we mainly attend in a developmental process. 



iv. The developmental organization is a specific complex of 

 potentialities. 



The fully developed organism which the ovum becomes has 

 parts — body and limbs, alimentary canal, etc., but these parts are 

 not, as such, in the structure of the ovum. In the terminology 

 of the current geneticist hypotheses we say that there are " genes '* 

 in the ovum which by interaction with each other, with the 

 cytoplasmic and external environmental materials and energies 

 give rise to the parts. But we cannot see, or otherwise know about 

 the genes (which, in cruder views, are regarded as ultra-micro- 

 scopic in size.) Plainly the ovum has the power, or potentiality 

 of becoming these parts when it interacts with its environmental 

 materials and energies. Of course, it becomes one whole, unitary 

 thing — the fully developed organism, but since different kinds 

 of organisms diflFer from each other in respect of one or more 

 characters, or parts, it is convenient to think about the potentiality 

 of the ovum as multiple, though it is sounder to think about it 

 as unitary. Thus we may, in exposition, speak about the organiza- 

 tion as a complex. 



And it is a specific complex in that it becomes an example of 

 a particular kind, or species, or race, etc., of organism. This 

 specificity of potentiality is in the organization and not in the 

 environment with which it interacts : thus cod and whiting eggs 

 develop in the same sea- water but one becomes a cod and another 

 a whiting. The environment conditions and limits the process 

 of development so that if these " external factors " are changed 

 the developmental process may also be changed. But these 

 external factors may be notably changed in many ways without 

 any corresponding developmental change except, perhaps, retard- 

 ation or acceleration of the period of incubation of the embryo. 

 We cannot, by any environmental change cause the cod-egg, for 



