THE METAZOA 



due the difference between the old order of 

 things and the new. Multiplication of 

 cells, all with fixed hereditary and specific 

 properties, was a great feature of the old 

 order, but each cell was then an independ- 

 ent and finished living thing. In the meta- 

 zoa, on the other hand, not independence 

 but interdependence of cells is the abso- 

 lute law. Their cells are never free unless 

 they are being cast out of the community. 

 A mere indefinite multiplication of their 

 cells, in which they are said to proliferate 

 indiscriminately, or even a sign of weaken- 

 ing of their reciprocal interdependence, 

 signifies disease and death. All their cells 

 instead are held together by a wonderful 

 something which " organizes " their de- 

 velopment along very definite lines. Thus 

 in the higher animals after the dividing 

 but adhering cells have come to resemble a 

 mulberry in appearance, a division into 

 three layers soon appears. From the first 

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