42 DOCTRINE OF DIFFERENTIATION 



embryo. Letting the fallacy of the argument pass, 

 I would comment on the root of it, viz., on the doctrine 

 of ' differentiation! according to which homogeneous 

 cells may be developed into this or that, or indeed 

 any structure ; a doctrine which Haeckel and others 

 advocate as a fundamental part of the theory of 

 Evolution. Like as men in a community, says Haeckel, 

 occupy themselves each in a different . employment 

 to the advantage of the whole, so the cells which 

 had become aggregated together to form a Syn- 

 amgebium, though originally homogeneous both in 

 substance and endowments, subdivided their labour 

 and engaged spontaneously in different modes of 

 action ; some metamorphosing themselves in one 

 I way, some in another, and, at the same time, acquir- 

 ing new endowments so as to be qualified for the 

 performance of new functions. 



This comparison would seem to imply that these 

 primaeval cells worked with both purpose and will, 

 in order to acquire new forms and new endowments, 

 thus promoting their own evolution. Our knowledge 

 of cells, however, does not warrant any such view of 

 their powers. We see only that cells run through 

 the different phases of development, growth, and 

 metamorphoses proper to them, each kind according 

 to its own destiny, and that they thus unconsciously 

 fulfil the purposes of their life. 



Granting any number of generations through 

 which cells may be supposed to have descended, 



