-¥I 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’ says— 
_ **Omnibus viventibus primordium insit, ex quo et a quo pro- 
- yeniant. Liceat hoc nobis primordium vegetale nominare ; nempe 
substantiam quandam corpoream vitam habentem potentid ; 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 
80 often quotes and of whom he speaks as his 
1 Exercitationes de Generatione. Ex. 62, ‘‘Ovum esse 
primordium commune omnibus animalibus.” 
