82 THE ASCENT OF MAN 



purposes to which the rooms are put, the perfection 

 with which each is adapted to its end, and the har- 

 monious co-operation among them with reference 

 to some common work. This also is the distinction 

 between a higher animal and a humble organism 

 such as the centipede or the worm. These creatures 

 are a monotony of similar rings, like a string of 

 beads. Each bead is the counterpart of the other ; 

 and with such an organization any high or varied 

 life becomes an impossibility. The fact that any 

 growing embryo is passing through a real develop- 

 ment is decided by the new complexity of structure, 

 by the more perfect division of labour, and of better 

 kinds of labour, and by the increase in range and 

 efficiency of the correlated functions discharged by 

 the whole. In the development of the human em- 

 bryo the differentiating and integrating forces are 

 steadily acting and co-operating from the first, so 

 that the result is not a mere aggregation of similar 

 cells, but an organism with different parts and 

 many varied functions. When all is complete 

 we find that one suite of cells has been specially 

 set apart to provide the commissariat, others have 

 devoted themselves exclusively to assimilation. The 

 ventilation of the house — respiration — has been 

 attended to by others, and a central force-pump 

 has been set up, and pipes and ducts for many 



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