220 EVOLUTION, OLD AND NEW. 



by the irritations and sensations and consequent exer- 

 tions of the parts previously existing, and to which the 

 new parts are to be attached.* 



****** 



* The embryon " must " be supposed to be a living 

 filament, which acquires or makes new parts, with new 

 irritabilities as it advances in its growth." t 



****** 



" From this account of reproduction it appears that 

 all animals have a similar origin, viz. a single living 

 filament; and that the difference of their forms and 

 qualities has arisen only from the different irritabilities 

 and sensibilities, or voluntaries, or associabilities, of 

 this original living filament, and perhaps in some degree 

 from the different forms of the particles of the fluids by 

 which it has at first been stimulated into activity." J 

 ****** 



" All animals, therefore, I contend, have a similar 

 cause of their organization, originating from a single 

 living filament, endued with different kinds of irritabi- 

 lities and sensibilities, or of animal appetencies, which 

 exist in every gland, and in every moving organ of the 

 body, and are as essential to living organism as che- 

 mical affinities are to certain combinations of inanimate 

 matter. 



" If I might be indulged to make a simile in a philo- 

 sophical work, I should say that the animal appetencies 

 are not only perhaps less numerous originally than the 

 chemical affinities, but that, like these latter, they change 

 with every fresh combination ; thus vital air and azote, 



* ' Zoonomia,' vol. i. p. 500. ,f Ibid. p. 501. \ Ibid. p. 502. 



