Sub-Kingdom I. PROTOZOA 
PROTOZOA are unicellular organisms, with bodies consisting of sarcode (proto- 
plasm), usually very minute, frequently microscopic in size, and without 
differentiated tissues or or gans. They are water-inhabitants, take in nourishing 
matter either at any point on the periphery of the body whatsoever, or 
through a so-called mouth (cytostome), and reject the undigested portions either 
from any part of the body whatsoever, or from a definite point called the anal 
aperture (cytopyge). The contractile sarcode almost invariably contains one or 
more nuclei, and exhibits considerable diversity of structure and differentiation. 
Locomotion is accomplished by means of vibratile cilia, flagella, pseudopodia, 
or irregular processes of the periphery. Reproduction takes place by means of 
budding or self-division, which latter process is often preceded by a temporary 
coalescence (conjugation) of two individuals. Protozoa are divided into four 
classes : Ehizopoda, Flagellata, Infusoria, and Gregarina (Sporozoa), of which only 
the first class is represented in the fossil state. 
Class 1. RHIZOPODA. 
Body-substance composed of richly granulated, jelly-like sarcode, which alternately 
protrudes, retracts, and again coalesces with irregular, finger-like, or thread-like 
processes. called pseudopodia. 
Rhizopods have been so named on account of the property they possess of 
protruding pseudopodia from the periphery of the body. Although serving as 
a means of locomotion and for the taking up of nutritive matter, the pseudo- 
podia represent no permanent organs, since they are protruded only for the 
passing occasion, and disappear again as they coalesce with the main body of 
sarcode. The ‘pseudopodia often exhibit protoplasmic streaming, and occa- 
sionally interlace so as to form networks. Rhizopods usually secrete calcareous, 
silicious, or chitinous tests, or build silicious skeletons of exceeding great 
diversity of form. Enormous deposits are built up by their accumulation 
on the sea-floor, and numerous strata of marine origin are largely composed 
of their remains. 
Four orders of Rhizopods are recognised: Foraminifera, Radiolaria, A moebina,? 
and Heliozoa , of these only the first two have parts capable of preservation. 
1 Biitschli, O., Protozoen in Bronn’s Classen und Ordnungen des Thierreichs, 1880-1889. 
2 To the Amoebina, Huxley and Haeckel formerly assigned the so-called Bathybius, a reticu- 
lated jelly-like substance composed of anastomosing strands, and occurring at great depths in the 
Atlantic Ocean. Wyville Thomson and Moebius regarded it as a precipitate of calcium sulphate, 
VOL. I Cc 
