OF THE FOETUS. 289 



fecoad foetus, which would neceflalily be a fe- 

 male, if the other was a male. All that could 

 happen in a cafe of this kind would be, thatfome 

 of the particles common to both individuals, being 

 equally attradled by the tirft centre of union, 

 murt: arrive there at the fame time, and produce 

 a monft^r, or a foetus with fuperiluous parts; 

 or, if fome of the common particles fliould fix 

 at too great a diftance from the firft centre, or be 

 conftraiiied by the attra(ltion of the fecond, round 

 which tb.e placenta is formed, a moniler, defec- 

 tive in fome part, would be the confequence. 



That the organic particles peculiar to the fex- 

 ual parts ferve for a bafis or centre of union to 

 the other particles of v>rhichthe embryo is form- 

 ed, 1 pretend not to demonftrate : But, as they 

 are the only particles which differ from the reft, 

 it is more natural to imagine that they Ihould 

 anfwer this purpofe than thole which are com- 

 mon to both individuals. 



I formerly detected the errors of thofe who 

 maintained, that the heart, or the blood, were firll: 

 formed. The whole is formed at the fame time. 

 We learn from adual obfervation, that the 

 chicken exills in the egg before incubation. 

 The head, the back-bone, and even the appcn- 

 daiges which form the placenta, are all dillin- 

 guilhablfc. 1 liave opened a great number of eggs, 

 both before and after incubation, a'id 1 am con- 

 vinced, from the evidence of my own eyes, that 

 the whole chicken cxifls, in the middle of the 



Vof-. If T cicatricc| 



