3o8 OF THE GRO\yTH, &c. 



and It is evident, that the latter derive their ori- 

 gin from the former. 



It is impolTible to determine the form of thefe 

 double parts before their expanfion, or in what 

 manner they are complicated, or u^iat figure 

 refults from their pofition in relation to the 

 fmgle parts. The body of an animal, at the 

 inftant of its formation, unqueftionably con- 

 tains all the parts of which it ought to be com- 

 pofed : But the relative difpofuion of thefe 

 parts is then very different from what after- 

 wards appears. - If we examine the expanfion 

 of a young leaf of a tree, we will find that it is 

 plaited on each fide of the principal nerve ; and 

 that its figure, at this tinie, has no refemblance 

 to that which it afterwards affumes. When we 

 amufe ourfelves with plaiting paper, in order to 

 give it the form of a crown, of a boat, &c. the 

 different plaits of the paper feem to have no re- 

 femblance to the figure which refults from their 

 expanfion : We only perceive that the plaits 

 are uniformly made in a certain order and pro- 

 portion, and that, whatever is done on one fide, 

 is alfo done on the other. But, to determine 

 the figures which may refult from the expan- 

 fion of any given number of folds, is a problem 

 beyond the powers of geometry. The fcience 

 of mathematics reaches not what immediately 

 depends upon pofition. Leibnitz's art of Jina- 

 lyfis fitus does not yet exift ; though the art of 

 knowing the relations that refult from the pofi- 

 tion 



