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EVOLUTION IN BIOLOGY 197 



is evolved from a particle of matter in which no 

 trace of the distinctive characters of the adult 

 form of that living thing is discernible. This 

 particle is termed a germ. Harvey 1 says 



"Omnibus viventibus primordium insit, ex quo et a quo pro- 

 veniant. Liceathoc nobfaprimofdiwft vcgetale nominare ; nempe 

 substantial!! quandam corpoream vitam habentem potentia ; vel 

 quoddam per se existens, quod aptum sit, in vegetativam 

 formam, ab interno principio operante, mutari. Quale nempe 

 primordium, ovum est et plantarum semen ; tale etiam vivi- 

 parorum conceptus, et insectorum vermis ab Aristotele dictus : 

 diversa scilicet diversorum viventium primordia. " 



The definition of a germ as " matter potentially 

 alive, and having within itself the tendency to 

 assume a definite living form/' appears to meet 

 all the requirements of modern science. For, 

 notwithstanding it might be justly questioned 

 whether a germ is not merely potentially, but 

 rather actually, alive, though its vital manifesta- 

 tions are reduced to a minimum, the term 

 " potential " may fairly be used in a sense broad 

 enough to escape the objection. And the quali- 

 fication of " potential " has the advantage of 

 reminding us that the great characteristic of 

 the germ is not so much what it is, but what it 

 may, under suitable conditions, become. Harvey 

 shared the belief of Aristotle whose writings he 

 so often quotes and of whom he speaks as his 



1 Exercitationes de Generatione. Ex. 62, "Ovum esse 

 primordium commune omnibus animalibus. " 



