EVOLUTION MADE TLAIN 
17 
CONNECTING LINKS 
There is a greater unity of all life than the 
many divisions and sub-divisions of the analyst 
would seem to warrant. The dividing lines be-' 
tween the different classes, orders, families 
and species are more apparent than real, the 
barriers of separation not so impassable as 
appear at first sight. 
To begin at the bottom, there is no hard and 
fast line drawn between living and non-living 
matter—or at least it is not always easy to say 
where the line should be drawn. Tyndall says, 
“The tendency of modern science is to break 
down the wall of partition between the organic 
and the inorganic, and to reduce both to the 
operation of forces which are the same in kind, 
but which are differently compounded.” 
Passing on to the first grand division of life, 
it would seem that nothing could be plainer 
than the line of cleavage between vegetable and 
animal life. Yet there is a twilight zone be¬ 
tween the two where each shades off toward 
the other, and which is inhabited by several 
living species of so doubtful a nature that sci¬ 
entists cannot agree as to which of the two 
great kingdoms they belong. These doubtful 
organisms are claimed by both the botanist 
and the geologist and are described in the text¬ 
books of both. Really they do not belong to 
either division, but are simply organisms that 
have not risen in the scale of life to the diverg¬ 
ing point of the animal and vegetable kingdoms. 
Ascending the animal scale we come to the 
line separating the invertebrates from the ver- 
