PLANTS AND ANIMALS DISTINGUISHED. 91 
giving out their own. Organized bodies, moreover, pass 
through a cycle of changes—growth, development, and _ re- 
production. Of more complex constitution, they are more 
unstable, and are more liable to decomposition than most 
inorganic compounds. The action of heat is invariably 
destructive. At the end of a certain period, fixed for each 
species, living bodies infallibly perish. 
CHAPTER II. 
PLANTS AND ANIMALS DISTINGUISHED. 
Ir may seem an easy matter to draw a line between 
plants and animals. Who can not tell a Cow from a 
Cabbage? Who would confound a Coral with a Mush- 
room? Yet it is impossible to assign any absolute, dis- 
tinctive character which will divide the one mode of life 
from the other. The difficulty of defining an animal in- 
creases with our knowledge of its nature. Linnzeus de- 
fined it in three words; a century later, Owen declared 
that a definition of plants which would exclude all ani- 
mals, or of animals which would not let in a single plant, 
was impossible. Each different character used in drawing 
the boundary will bisect the debatable ground in a differ- 
ent latitude of the organic world. Between the higher 
animals and higher plants the difference is apparent; but 
when we reflect how many characters the two have in 
common, and especially when we descend to the lower 
and minuter forms, we discover that the two “ kingdoms” 
touch, and even dissolve into, each other. This border- 
land has been as hotly contested among naturalists as 
many a disputed frontier between adjacent nations. Its 
inhabitants have been taken and retaken several times by 
