EVIDENCES OF ORGANIC EVOLUTION 31 



do better than recapitulate, with only slight modifi- 

 cations, the arguments there given : 



1. THE GRADATION OF ORGANISMS. Both in the 

 animal and vegetable kingdoms we may trace, in spite 

 of certain gaps, a long series of gradations in com- 

 plexity of structure, so that between the simplest and 

 the most complicated of living things a great number 

 of intermediate stages are to be found. When we 

 pass to the lower end of the scale in either case, we 

 come upon a group of creatures of comparatively 

 simple organization. Among them we find members 

 with regard to which we cannot definitely say that 

 they are either animals or plants. Moreover, these 

 unicellular organisms resemble in many ways the 

 egg-cell from which every individual among the higher 

 animals and plants originates. 



It is true that we now know it to be quite impossible 

 to dispose all the members of the animal kingdom in 

 a single linear series, such as was formerly suggested, 

 passing in orderly sequence from the amoeba up to 

 man. ' Instead of regarding living things as capable 

 of arrangement in one series, like the steps of a ladder, 

 the results of modern investigation compel us to dis- 

 pose them as if they were the twigs and branches of a 

 tree. The ends of the twigs represent individuals, 

 the smallest groups of twigs species, larger groups 

 genera, until we arrive at the source of all these 

 ramifications of the main branch, which is represented 

 by a common plan of structure/ 



2. EMBRYOLOGY. All the members of a particular 

 group of animals or plants as a rule resemble one 



