DESCENT OF MAN FROM SOME LOWER FORM. 145 



at most only four or five progenitors, and plants from an 

 equal or lesser number. 



Analogy would lead me one step further, namely, to 

 the belief that all animals and plants are descended from 

 some one prototype. But analogy may be a deceitful 

 guide. ^Nevertheless, all living things have much in com- 

 mon, in their chemical composition, their cellular struct- 

 ure, their laws of growth, and their liability to injurious 

 influences. "We see this even in so trifling a fact as that 

 the same poison often similarly affects plants and ani- 

 mals ; or that the poison secreted by the gall-fly produces 

 monstrous growths on the wild-rose or oak-tree. "With 

 all organic beings, excepting, perhaps, some of the very 

 lowest, sexual reproduction seems to be essentially simi- 

 lar. With all, as far as is at present known, the germinal 

 vesicle is the same ; so that all organisms start from a 

 common origin. If we look even to the two main divis- 

 ions — namely, to the animal and vegetable kingdoms — 

 certain low forms are so far intermediate in character 

 that naturalists have disputed to which kingdom they 

 should be referred. As Professor Asa Gray has re- 

 marked, "the spores and other reproductive bodies of 

 many of the lower algae may claim to have first a charac- 

 teristically animal, and then an unequivocally vegetable 

 existence." Therefore, on the principle of natural selec- 

 tion with divergence of character, it does not seem in- 

 credible that, from some such low and intermediate form, 

 both animals and plants may have been developed ; and, 

 if we admit this, we must likewise admit that all the 

 organic beings which have ever lived on this earth may 

 be descended from some one primordial form. But this 

 inference is chiefly grounded on analogy, and it is imma- 

 terial whether or not it be accepted. 



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