130 THE LESSON OF EVOLUTION 



biophores. For why should they congregate to- 

 gether? If we look to the larger operations of bio- 

 logical evolution for a clue to guide us, we see some 

 resemblance between this clustering of certain 

 biophores and the action of preferential selection 

 in forming groups. But preferential selection is a 

 mental operation, and so, possibly, may have been 

 the formation of the nucleus. I suppose it to be 

 the concentration of mind in the cell ; that is the 

 formation of a cell-brain. We see a further develop- 

 ment of the same kind in the formation of the cen- 

 trospheres and the differentiation of the nuclear 

 plasm. These were the first steps in co-operation 

 for mutual benefit, which led to the physiological 

 division of labour, which Professor H. Milne- 

 Edwards was the first to explain. 



This hypothesis may seem fanciful, even wild ; but 

 the phenomena are very extraordinary, and the 

 explanation, no doubt, will be extraordinary also. 

 And I think that, after duly weighing the evidence' 

 that can be brought forward, the reader will find 

 that the hypothesis is more reasonable than appears 

 at first sight. Let us look at some of the evidence.. 



Take the contractile vacuole found in the ectosarc 

 of the Protozoa. In Amoeba it is a simple cavity, 

 which gradually increases in size, filling up with 

 water, until it suddenly contracts and disappears. 

 Then, after an interval, it again reappears in the 

 same place, and slowly expands once more. This 

 contractile vacuole is thought to be an excretory 

 organ , as uric acid is said to have been detected in 

 it. When the Amoeba undergoes fission the 



