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where a single individual animal is constituted by a single 
cell, we may take the Amoeba or Proteus- Animalcule. This 
little microscopic creature, so common in water holding 
organic matter in solution, consists of a minute mass of proto- 
plasm, which does not possess any rigid, well-defined, or un- 
yielding outer investment, but is so far differentiated that it 
can be clearly distinguished into an outer transparent layer, 
or ectosarc,” and an inner more fluid and mobile molecular 
layer, or cc endosarc.” Not only is this differentiation of the 
protoplasmic body a distinct advance upon what obtains in 
the Monera , such as Protomyxa, but there is now the further 
feature that there exists in the endosarc a solid granular 
“ nucleus; ” In addition, also, to numerous fluid-cavities 
or “vacuoles,” we now meet with a permanent internal circu- 
latory organ, in the form of what is known as a “ contractile 
vesicle.” This is a little cavity or vesicle, holding a fixed 
position, filled with a colourless fluid apparently derived 
from the digestion, and exhibiting rhythmical movements of 
contraction and dilatation. It may, in fact, be regarded as a 
rudimentary heart. No mouth is present, nor are there any 
digestive organs ; while the nervous and reproductive systems 
are wholly undeveloped. Owing to the absence of a hard 
outer covering, the soft protoplasm of the body is amenable 
to the slightest external stimulus, and can be protruded from 
all points of the surface in the form of temporary outward 
prolongations or pseudopodia, which are used as organs of 
prehension, and are employed by the animal as the agents 
whereby it obtains its food. The pseudopodia of the Amoeba 
are, in fact, precisely similar in their essential structure and 
function to the structures known by the same name in the 
Protomyxa, but they are now comparatively few in number, 
and are blunt and finger-shaped in form. The Amoeba can 
reproduce itself either by an actual division of its substance 
into two portions, each of which ultimately becomes an in- 
dependent being, or by means of a process of “ ency station,” 
and endogenous division, the little sarcode-spherules formed 
within the parent cyst being ultimately set free by the rupture 
of the latter to give origin to new individuals. 
Nearly allied to the Amoeba are the wonderful organisms 
known as Foraminifera and Polycystina, which among other 
peculiarities, exhibit the feature that the soft sarcode of the 
body, undifferentiated as it is, has the power of secreting hard 
structures of the nature of a skeleton, often of surpassing 
beauty and not unusually of mathematical regularity. In the 
case of the Foraminifera, which are so abundant in our present 
oceans, and enter so largely into the composition of the 
