Life and Its Conditions. It 
or even impossible, to decide with positiveness whether we 
are dealing with a plant or an animal. In the higher orders 
of the two kingdoms there is no difficulty in reaching a 
decision, the higher animals being readily separated from the 
higher plants by the possession of a nervous system, of a 
locomotive power which can be voluntarily exercised, and of 
an internal cavity adapted for the reception and digestion of 
solid food. No so-called nervous system or organs of sense 
are possessed by the higher plants, although some of them 
doubtlessly manifest conscious and intelligent action, nor 
are they capable of voluntary changes of place, nor provided 
with any definite internal cavity, their food being generally 
fluid or gaseous. 
Descending the scale to the very bottom, we reach a class 
of animals, the Protozoa, which cannot be separated in many 
cases from the Protophyta by these distinctions, since many 
of the former have no digestive cavity, nor the slightest trace 
of a nervous system, while many of the latter possess the 
power of active locomotion. As to external configuration, no 
certain rules can be laid down for separating animalsand plants, 
many of the lower plants, either in their earlier stages, or in 
their maturity, being exactly similar in form to some of the 
lower animals. This is the case with some of the Alge, 
which resemble very closely in form certain Infusorian ani- 
malcules. Again, many undoubted animals, which are 
rooted to solid objects in their adult state, are so plant-like 
in appearance as to be popularly regarded as vegetables. 
The Sea-firs, and the more highly organized Flustras or Sea- 
mats, which are usually considered as sea-weeds by sea-side 
visitors, are a few of many examples that might be taken 
from the so-called Hydroid Zodphytes. No decided distinc- 
tion between animals and plants can be drawn as to their 
minute internal structure, both alike consisting of molecules, 
of cells, or of fibres. Some decided, though not universal, 
differences exist in chemical composition. Plants exhibit a 
decided predominance of ternary compounds, or compounds 
