_ DIATOMS 38 
it was a moot question whether they are animals or 
plants; and the echo of that dispute has but just died 
away. This may seem somewhat strange, as between 
animals and plants of the usual type, the difference is 
readily seen. Their respective characteristics are known 
to the most heedless. But with those objects whose life 
is confined to the limits of a single cell, biologists have 
been taxed to tell plant from animal. Their task to draw 
a sure line of distinction has been as hard as it would be to 
to put lines of separation betwixt the colors of the rainbow. 
After exploring the great circle of living beings, 
Linnzeus formulated the dictum that nature takes no leaps ; 
and discoveries since the days of the great Swedish 
naturalist confirm his saying, and extend its meaning 
beyond the limits to which he applied it. Many of 
these units of vegetabie life are self-moving, a faculty 
formerly considered to be distinctively animal. But 
numerous traits of these single-celled organisms are 
anomalous and equivocal. Common signs altogether fail 
in distinguishing monocellular animals from plants ; and 
the best tests for that purpose are difficult to apply, and 
are imperfect. To most men it is of but little use to know 
that an orgatiism is vegetable if there be starch in its cell; 
or if it evolves oxygen and absorbs nitrogen ; or if from 
the medium it lives in, it can take oxygen, hydrogen, nitro- 
gen and carbon, and can turn them into albumen and kin- 
dred compounds, without ingesting them in a stomach, In 
truth these organisms are so minute, and the tests sug- 
gested are so delicate, that we prefer to take on trust con- 
clusions as to their biological rank ; and are fain to know 
that whether we call one of these atomies zoophyte or 
phytozoon —animal-like plant, or plant-like animal—the 
marvels of its life-history in either case are the same. 
In 1868 Haeckel proposed to supplement the zoological 
nomenclature of that day, with a new sub-kingdom to be 
called Protista. Under that name he grouped all classes of 
