Chap. 42.] Theories of Bttffon and SpalanzanL 40$ 

 It is in ibme meafure foreign to the objects of the 

 prefent work to enter on thofe theories with which phi- 

 lofophers have amufed themfelves and their readers 

 concerning the generation of animals. Independent of 

 the indelicacy of the fubject, there is another ftrong ob- 

 jection to their introduction here ; fince thefe theories 

 reft upon no other foundation than conjecture, and 

 fome fallacious, and, I think, delufive microfcopical 

 obfervations. I mall, therefore, content myfelf with 

 referring the reader to the natural hiftory of the Count 

 de Buffbn, and for a direct contradiction of his theory 

 to the Abbe Spalanzani. The former of thefe philo- 

 fophers has derived the principle of animal exiftence 

 from the male, and the latter from the female. The 

 generation of fifties appears, indeed, greatly to favour 

 the theory of Spalanzani, for in that inftance at leaft, 

 the rudiments of the young animals appear to be con- 

 tained in the eggs or roe, which the female fifh firft 

 depofits j and the milt which is afterwards depofited 

 by the male appears only to excite them into action 

 and growth. If we admit thus much of his theory, 

 however, we muft attend him a ftep further, and fup- 

 pofe that every female ovum in the ovarium of a female 

 muft itfelf contain ovaria and ova, and by extending 

 the fame idea we muft be led to conclude, that the 

 rudiments of all the animals, which have exifted, do 

 exift, or ever will exift, were originally contained in 

 the ovarium ofithe firft female of the particular fpecies 

 to which they refpectively belong. This has been 

 therefore called the theory of involution, and has been 

 fuppofed equally applicable to animals and vegeta- 

 bles. 



In the procefs of generation, the firft marks we fee, 



after impregnation, of the future progeny, is a minute 



being without limb or feature, connected by a cord to 



D d 3 th<- 



