Natural History of the Animalcules, tn 
tainly ascertained, but it seems to be the seat of all 
reproductive changes. 
If continuous observation of the organism be made, it 
will at times be noticed that a protrusion or pseudopo- 
dium becomes detached, and that this becomes by growth 
another Amceba ; or that the body divides into two 
parts, each part growing into a perfeft Animalcule ; or 
that the entire organism draws in its pseudppodia, becomes 
rounded and cyst-like, and remains quiescent for a certain 
time, in what is called its encysted state, ultimately 
treeing itself again after its period of rejuvenescence. 
The Proteus-animalcule affords a good example of 
the unicellular organisms. It consists of one small 
mass of independent protoplasm ; and when this divides 
into two portions, these do not remain attached to each 
other to form a bi-cellular organism, but separate and 
lead independent lives. It may be taken as a special 
type of the class of organisms know r n as Rhizopoda or 
Root-footed Animalcules — the name being given in allu- 
sion to the pseudopodia or false-feet. In this simple type 
I of life, no sense or nervous organs, no digestive organs, 
i no muscular organs, no generative organs are to be found ; 
; yet all its vital processes are performed satisfa&orily to 
♦ itself. It lives, it grows, it feels, it moves, it reproduces 
its like ; and the one cell is the seat of all these pheno- 
mena, the explanation of which is to be found in the fa6t 
- that these are, above all, the essential charafteristics of 
| protoplasm, that " physical basis of lite n of which the 
cell is composed. 
A peculiar interest attaches to this type in the fa6l that 
if the blood or nutrient fluid of all the higher animals be 
examined, it will be found to consist, either in part or 
