408 ANIMAL REPRODUCTIONS. 
ly ufe very fcientific expreffions, but to which no: 
diftin& idea can be attached(1). It is not 
enough to fay, an effect is produced by a certain 
power: it muft be demonftrated how we con- 
ceive the effect depends on the power: and, by 
admitting the exiftence of the caufe, to give a fa- 
tisfactory explanation of the principal peculiari- 
ties which the effect prefents. Now, when we- 
fay aleg or an arm is produced by the vege- | 
tative, or any other power, who can be fenfi- 
ble how the exiftence of the limb naturally arifes 
from fuppofing the power? Phyfical powers do 
not prefent their own limits: for any power is in 
itfelf indeterminate. -How could the imaginary 
vegetative power determine the produétion of a 
leg rather than an arm, which it might juft as 
readily 
(1) The powers of relation were conceived by M. de 
Maupertuis. His ingenious work, La Venus Phyfique, 
mutt be confulted for underftanding how he ufes them in. 
explaining the myfteries of generation. 1 
The vegetative or Expanfive power was created by Mr 
Needham. 
M. Wolf, Profeflor of Anatomy in Peterfburgh, en- 
deavoured to introduce the efential force into organic na- 
ture. An account of his hypothefis may be feen, Art.. 
334, Corps Organifés, Note. 
Drsgatic Molecules are M. de Buffon’s favourite hypo- 
thefiss 
