n] BIOLOGICAL FOUNDATIONS 61 



architectural metaphor may help us. Life finds in 

 the cell the ground-plan for her first mansion a 

 one-roomed hut. You may change your one-roomed 

 plan from round to square, from square to oblong, 

 and you will not have improved it: but add a 

 chimney and windows, and at once, though still but 

 one room, it is something better. Even a church 

 with its aisles and nave, transepts and choir has grown 

 thus by internal differentiation. In essence it must 

 always be a single room so that the congregation 

 may see and hear the service; and we realize the 

 justice with which the Romans used aedes in the 

 singular to mean a temple. 



With equal justice they used the plural for a 

 house. They had reached the stage of civilization 

 when a house was no longer a single room, serving 

 more ends than one at once, and all in turn, but a 

 collection of rooms, each one different from any old 

 single-roomed house, all modified in their architecture 

 from being thus built up into a common whole, but 

 none the less obviously separate rooms, each in itself 

 a unit, each somehow comparable with the single 

 space of the more primitive dwelling. This way, of 

 joining unit with unit, is the third way with organic 

 change. Suppose that instead of separating from 

 each other after each division, the cells remain con- 

 nected. The result will be a colony of cells each one 

 like all its fellows. If division of labour sets in later 



