108 PHLYUM PROTOZOA—THE SIMPLEST ANIMALS. 
B. Predominantly amceboid Protozoa.—Rhizopoda.—The 
simplest Rhizovods generally resemble Amada, and are ranked in the 
class (3) Lobosa, They may reproduce simply by division, as does 
Ameba itself, or may liberate several buds at once (Avcel/a), or form 
spores which conjugate (Pelomyxa). Warious forms, such as A7cella, 
are furnished with a shell. 
(4) The Labyrinthulidea are represented by forms like Labyrznthula 
on Algee, and Chlamydomyxa on bog-moss, which consist of a mass of 
protoplasm spread out into a network, and of numerous spindle-shaped 
units, which travel continually up and down the threads of the living 
net. 
Fic. 49.—Formation of shell in a simple Foraminifer. 
—After Dreyer. 
In A the shell has one chamber ; B, C, and D show the formation 
of asecond. Note outflowing psuedopodia and the enclosure of 
the shell by a thin Jayer of protoplasm; note also the nucleus 
in the central protoplasm. 
As (5) Heliozoa are classified the sun-animalcules (Actenospherium, 
Actinophrys sol), and others, in which there are stiff processes radiating 
froma spherical body. Reproduction may be by division or by spore 
formation ; skeletal structures may be represented by spicules. 
The (6) Foraminifera or Reticularia include an interesting series 
of shelled forms in which the peripheral protoplasm forms branching 
interlacing threads. A few simple forms occur in fresh water ; the great 
majority occur on the floor of the sea at varying depths; some 
