4 THE FLOWERING PLANT. 
which they reduce to solution, often in a kind of external stomach 
(e.g., pitchers of the pitcher plant). On the other hand, some 
animals, all rather low in the scale, contain chlorophyll, and by 
its means utilize the carbon dioxide of the air and simple salts 
dissolved in the water around them; and it is not unlikely that 
animals exist which contain so much chlorophyll as to obviate 
altogether the necessity for solid food. Some moderately high 
annals, such as the tapeworm, which are not green, can dispense 
with such food in another way. ‘They live as endo-parasites, 2.., 
within other animals, and feed at their expense on the soluble 
products of digestion, which, however, are by no means simple in 
composition. This mode of life may, and often does, do away 
with the necessity for an internal digestive cavity, as in the 
example quoted. 
The branching form and absence of locomotor powers cease to 
be plant-tests among many microscopic forms, which may be oval 
or spherical, and capable of the most active locomotion. And 
many comparatively high animals (oyster, &c.) are sedentary, 
though their embryos swim actively about. There is no trace of 
a nervous system in the lowest animals; and, lastly, cellulose is 
not exclusively a vegetable product. It is found in some few 
animals, as, @.g., the sea-squirts (Ascidians). 
But in spite of these partial exceptions, there is no difficulty 
whatever in distinguishing plants from animals, except in the 
very lowest forms. These are believed to be nearer a common 
stock from which all organisms have sprung, and are, therefore, 
more alike than are the higher plants and animals, which have 
diverged more or less in different directions from that stock. 
Differences between Living and Non-Living Matter.—At this 
point the question naturally arises, ‘“‘ How does organic living 
matter differ from imorganic non-living matter?” Here, so far 
as we yet know, sharp boundary-lines can be drawn. 
(1.)! The elementary chemical substances, some seventy in num- 
ber, are supposed to be ultimately made up of infinitely minute 
particles, atoms. Even in an element, these are built up into 
small aggregates or molecules, while the molecules forming che- 
mical compounds are built up from more than one kind of atom, 
and are the smallest quantities in which a compound can exist 
as such. When a very large number of atoms enter into a 
molecule, it is said to be complex, and this is characteristic of 
the compounds of which organisms are composed. All plants and 
animals are essentially made up of a jelly-like substance, known 
as protoplasm, which is undoubtedly of extreme complexity. 
1 Students who have read no chemistry are strongly ae to work through 
such a book as Roscoe’s Primer. 
