290 EVOLUTION IN BIOLOGY. 



I. The Evolution of the Individual. 



JSTo exception is, at this time, known to the general 

 law, established upon an immense multitude of direct 

 observations, that every living thing is evolved from a 

 particle of matter in which no trace of the distinctive 

 characters of the adult form of that living thing is dis- 

 cernible. This particle is termed a germ. Harvey* 

 says 



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

 veniant. Liceat hoc nobis primordium vegetale nominare ; nempe 

 substantiam quandam corpoream vitam habentem potentia; vel 

 quoddam per se existens, quod aptum sit, in vegetativam formam, 

 ab interne) principio operante, mutari. Quale nempe primordium, 

 ovum est et plantarum semen ; tale etiam yiviparorum conceptus, 

 et insectorum vermis ab Aristotele dictus: diversa scilicet diver- 

 sorum viventium priinordia." 



The definition of a germ as " matter potentially alive, 

 and having within itself the tendency to assume a defi- 

 nite living form," appears to meet all the requirements of 

 modern science. For, notwithstanding it might be just- 

 ly questioned whether a germ is not merely potentially, 

 but rather actually, alive, though its vital manifestations 

 are reduced to a minimum, the term " potential " may 

 fairly be used in a sense broad enough to escape the 

 objection. And the qualification of " potential " has the 

 advantage of reminding us that the great chacteristic of 

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

 under suitable conditions, become. Harvey shared the 



* " Exercitationes de Generatione." Ex. 62, " Ovum esse primordium 

 commune omnibus animalibus." 



