Sect. XXXIX. 4. 5. GENERATION. 39 i 



This idea of the growth of the embryon accords alfo with tKc 

 production of fbme monftrous births, which confift of a duplica- 

 tive of the limbs, as chickens with four legs ; which could not 

 occur, if the fetus was formed by the diftention of an original 

 ftamen, or miniature. For if there mould be a fuperfluity of 

 the firft nutritive particles laid up in the egg for the firft living 

 filament ; it is eafy to conceive, that a duplicature of fome parts 

 may be formed. And that fuch fuperfluous nouriiliment fome- 

 times exifts, is evinced by the double yolks in fome eggs, which 

 I fuppofe were thus formed previous to their impregnation by the 

 exuberant nutriment of the hen. 



This idea is confirmed by the analogy of the monfters in the 

 vegetable world alfo 9 in which a duplicate or triplicate produc- 

 tion of various parts of the flower is obfervable, as a triple necta- 

 ry in fome columbines, and a triple petal in fome primrofes ; 

 and which are fuppofed to be produced by abundant nourrfh- 

 ment. 



5. If the embryon be received into a fluid, the ftimulus of 

 which is different in fome degree from the natural, as in the 

 production of mule-animals, the new irritabilities or fenfibilities 

 acquired by the increasing or growing organized parts may differ, 

 and thence produce parts not fimilar to the father, but of a kind 

 belonging in part to the mother ; and thus, though the original 

 ilamen or living ens was derived totally from the father, yet new- 

 irritabilities or fenfibilities being excited, a change of form cor- 

 Tefponding with them wrfl be produced. Nor could the pro- 

 duction of mules exift, if the ftamen or miniature of all the 

 parts of the embryon is previoufly formed in the male femen, 

 and is only diftended by nourifhment in the female uterus. 

 Whereas this difficulty ceafes, if the embryon be fuppofed to 

 confift of a living filament, which acquires or makes new parts 

 with new irritabilities, as it advances its growth. 



The form, folidity, and colour, of the particles of nutriment 

 , laid up for the reception of the firft living filament, as well as 

 their peculiar kind of ftimulus, may contribute to produce a dif- 

 ference in the form, folidity, and colour of the fetus, fo as'to re- 

 femble the mother, as it advances in life. This alfo may es- 

 pecially happen during the firft ftate of the exiftence of the 

 embryon, before it has acquired organs, which can change thefe 

 iirft nutritive particles, as explained in No. 5. 2. of this Section. 

 And as thefe nutritive particles are fuppofed to be fimilar to 

 thofe, which are formed for her own nutrition, it follows that 

 the fetus fhould fo far refemble the mother. 



This explains, why hereditary difcafes may be derived either 

 from the male or female parent, as well as the peculiar form of 



•s.ither 



