EXTENSION OF EVOLUTIONARY THEORIES 353 



stage that protoplasm is fluid. Thus the form of the 

 lowest organisms may be compared to that of a drop 

 of water. The shapes of other protozoa are explained 

 by the membranes that cover them, which cause the 

 departures from the globular form by their inequality 

 in thickness and extensibility. The forms of the lowest 

 organisms are, therefore, parallel to forms in the 

 inorganic world. In fact, in the latter there are forms 

 that are far more difficult to understand than those of 

 the protozoa the crystals. 



But how do we explain the forms of the higher 

 organisms ? 



We have seen that these forms have been developed 

 from the lower ones. No extraordinary forces were 

 employed in this evolution ; the new organisms 

 were in each case the outcome of an accidental, local 

 coincidence of physico-chemical conditions. 



But is not chance itself incapable of being understood 

 mechanically ? 



No. Chance, in our sense of the word, has nothing 

 to do with the miraculous. Every accident, on which 

 we count, is the ultimate effect of a whole chain of 

 successive causes and effects, in all of which only 

 natural forces are at work. We are, therefore, quite 

 convinced that " chance " is to be explained physico- 

 chemically ; though we grant that the causes which 

 have determined it are not known to us. We have an 

 excellent illustration of the matter in a ball that has 

 been thrown on the ground. Chance determines at 

 what spot it will stop rolling ; in other words, the spot 

 cannot be calculated in advance, because the various 



