44 A Century of Science 



the development of the ovum the change from 

 homogeneity to heterogeneity is accompanied by a 

 change from indefiniteness to definiteness ; there 

 are segregations of similarly differentiated units 

 resulting in the formation of definite organs. He 

 further showed that there is a parallel and equally 

 important change from incoherence to coherence ; 

 along with the division of labour among the units 

 there is an organization of labour : at first, among 

 the homogeneous units there is no subordination, 

 to subtract one would not alter the general as- 

 pect ; but at last, among the heterogeneous organs 

 there is such subordination and interdependence 

 that to subtract any one is liable to undo the whole 

 process and destroy the organism. In other words, 

 integration is as much a feature of development 

 as differentiation ; the change is not simply from 

 a structureless whole into parts, but it is from a 

 structureless whole into an organized whole with 

 a consensus of different functions, and that is what 

 we call an organism. So while Baer said that the 

 evolution of the chick is a change from homoge- 

 neity 'to heterogeneity through successive differen- 

 tiations, Mr. Spencer said that the evolution of 

 the chick is a continuous change from indefinite 

 incoherent homogeneity to definite coherent het- 

 erogeneity through successive differentiations and 

 integrations. 



