OF THE FOETUS. 309 



tion of things would be, perhaps, more ufefiil 

 than that which has magnitude only for its oh- 

 jed:; for we have more occafion to be acquaint- 

 ed with form than with matter. 



In the expanfion of natural produdions, the 

 folded or plaited parts not only afl'ume different 

 pofnions, but they acquire, at the fame time, ex- 

 tenfion and folidity. Since, therefore, we are 

 unable to afcertain the exad: refult of a fnnple 

 expanfion of a folded figure, in which, as in 

 folded paper, nothing takes place but a change 

 of pofition among the parts, without any aug- 

 mentation or diminution of the quantity of 

 matter, how is it poflible for us to judge con- 

 cerning the expanfioil of the compound body of 

 an animal, in which not only the relative pofi- 

 tion, but likewife the quantity of matter in thefe 

 parts, fuffer conliderable changes ? We can only 

 re;ifon, therefore, on this fubjed, by drawing 

 conclufions from the examination of cbjeds at 

 ■different periods of their expanfion. 



We, indeed, perceive the chick in the egg 

 before incubation : It fwims in a tranlparent 

 Huid, contained in a fmall purfe iornicd by a 

 very fine membrane in the centre of the cica- 

 trice. But the chick is then only a particle of 

 inanimatcd matter, in wliich no organization or 

 determined figure can be didinguiriied. We can 

 perceive, however, tliat one of its extremities is 

 the head, and the other the back-bone. 7 he 

 ;mbiyo, in this flatc, fecms to be the firft pro- 



U 3 dua 



