FRESH-WATER ALG. 195 
By the fresh-water conferve we are brought to 
the very boundaries of the inscrutable ; into those 
arcana of nature where life, reduced to its simplest 
expression, seems invested with a deeper and more 
thrilling mystery. They are the very lowest in 
the scale of vegetation, and approximate so closely 
to certain animals both in form and in vital func- 
tions, that the best naturalists are unable to draw 
the line of distinction between their simplest 
species and the humblest animal organisms, or, 
indeed, to determine whether they possess vitality 
or not. They confound and neutralize the old 
arbitrary definitions of the three kingdoms of 
nature. Neither the power of voluntary motion 
nor chemical composition can be called the char- 
acteristic by which they are separated from ani- 
mals; nor can mere appearance or ostensible 
mode of production be regarded as sufficient to 
distinguish them from minerals. All we can say 
regarding them, and regarding the animals with 
which they form connecting links, and into which 
some even say they are transmuted, being animals 
at one period of their lives and vegetables at an- 
other, is merely that the two lines or systems of 
life seem to start as it were from a common point 
at the base; the inferior forms bearing a certain 
similarity to each other in structure and functions, 
which gradually disappears as we ascend the scale 
