DESCENT OF MAN FEOM SOME LOWER FOBM. 145 



at mo st only four or fire progenitors^ and plants from an 

 eqna l or les ser'nnmbef. 



Analogy would lead me one step further, namely, to 

 tlie belief that all animals and plants are descended from 

 some one prototype. But analogy may be a deceitful 

 guide. Neyertheless, all living things have much in com- 

 mon, in their chemical composition, their cellular struct- 

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

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

 the same poison often similarly afiects 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 o n this ea rth may 

 be descendedfrom some one. primordial fomi; 5jit..this 

 inference is chiefly grounded on analogy, and Jt_ ia i m m ar - 

 teriai whether or not it be accepted. 



