16 Tue Orrawa NaTurRALIST.. _- [April 
NOTES ON FRESH-WATER RHIZOPODS. 
By W. S. ODELL. 
Rhiozpods take rank in the Protozoa, the simplest and lowest 
of the grand divisions of the animal kingdom ; and are themselves 
divided into the following orders: Protoplasta, Heliozoa, Radio- 
laria, Foraminifera and Monera. he genera Radiolaria and Fora- 
mintfera are marine, and are of great geological importance. 
Chalk is composed largely of shells of the latter; while deep-sea 
ooze is mainly formed of shells of Radiolaria and Foraminifera. 
But these notes deal only with fresh-water forms, so it is unneces- 
sary to consider others here. g 
‘‘ What are Rizopods?” many willask. They are the lowest 
animals in the scale of life, and are mostly microscopic, the largest 
forms being just visible to the naked eye or with a good pocket 
lens. 
They consist of a soft mass of clear or granular jelly-like sub- 
stance called protoplasm (the primitive material from which or- 
ganic bodies are moulded) endowed with powers of motion, inges- 
tion, digestion, secretion, excretion and reproduction: functions 
which ordinarily distinguish animal lite of a higher order. The 
simplest kinds have no shell, but by far the greater number are 
provided with a shell-covering, frequently composed of grains of 
quartz sand, diatom cases, or sponge spicules, cemented together, 
exhibiting great variety in form, construction, and arrangement 
of stucture, often remarkable for great beauty. A description of 
a species of Ameeba, viz., A. proteus, Rosel, the earliest described, 
and familiar to students of Natural History, only can be given here. 
Amoeba is invisible to the naked eye, rarely exceecing 4%mm. 
(;4 in.) in diameter. Under the microscope it appears as a shape- 
less mass of jelly, nearly colorless; composed of two parts, 
the central granular, called the endosarc, and containing the nu- 
clei and contractile vesicles. Completely surrounding this is a 
transparent layer, or ectosarc. The animal is constantly changing 
its form. Often the changes are so slow as to be almost imper- 
ceptible but by examining at intervals, it will have altered so much 
