CONCLUSION 809 



lieve that animals_jij:a---xieseeiLded„ from at -most only 



four or fiveprogeuitors, 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 

 common, in their chemical composition, their cellular 

 structure, 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 animals; 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 similar. 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 divisions — namely, to the animal and 

 vegetable kingdoms — certain low forms are so far inter- 

 mediate in character that naturalists have disputed to 

 which kingdom they should be referred. As Professor 

 Asa Gray has remarked, "the spores and other repro- 

 ductive bodies of many of the lower algae may claim to 

 have first a characteristically animal, and then an une- 

 quivocally vegetable existence." Therefore, on the prin- 

 ciple of natural selection with divergence of character, 

 it does not seem incredible 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 



