THE SIMPLEST FORMS OF LIFE 385 
Most bacteria appear, under the microscope, as ex- 
tremely small, often apparently homogeneous bodies 
of various shapes—round, oblong, rod-shaped, etc. 
(Fig. 5). They frequently exhibit active move- 
ments which are due to the presence of excessively 
fine cilia. They multiply with extraordinary rapidity 
Fic. 5 (Schizophyta).— A, the tip of a filament of Oscillaria, one of the 
Fission Algz (Schizophycee). The cell is filled with granular proto- 
plasm, but no definite nucleus or plastids can be made out. B, part of 
a filament of Anabena, a fission alga, showing two sorts of cells; 
a, one of the “‘ heterocysts ’’ which separate the filament into segments; 
C, a water-plant with colonies of a fission alga (Gleotrichia), gi, grow- 
ing upon it; D, Beggiatoa, a form without chlorophyll, allied to Oscil- 
laria; E-H, different forms of Bacteria (Schizomycetes); E, typhus 
germ (Bacillus typhi); F, Tetanus bacillus (B. te¢ani), showing spore 
formation; G, cholera bacillus (Microspira comma); H, spirillum ru- 
brum; Gand Hare stained to show the cilia. (Figs. D-H after Migula.) 
by transverse fission, but may also produce internally 
special resting-cells, or spores (F). These latter 
are thick walled, and often capable of enduring an 
astonishing degree of heat without injury. Organic 
decomposition is mainly due to the activity of bacteria, 
and it is unnecessary to dwell upon the various forms 
