STUDIES AMONGST AMCEBJE. 
231 
granules in their rushes and streamings may alter the shape 
for a while ; there is no limiting or enclosing membrane, but in 
large Amoebae, where this contracting bladder or vesicle is very 
visible indeed, something like a rough edge appears within. Evi- 
dently the light traverses the spot more readily than it does the 
surrounding protoplasm, and this is due to its being filled with 
a more highly refracting medium — water. The water coming 
from somewhere collects as the protoplasm expands actively 
from a point-like space ; and then when it contracts more actively 
in a more or less observable rhythm, the water is expelled 
and goes somewhere. This pulsation, or what the doctors would 
call systole and diastole, occurring in a structureless material, 
is as incomprehensible as the outside change of shape, and the 
protrusion and retraction of the pseudopodia. The active ex- 
pansion would suck in water from the surrounding mass, and it 
appears to do so generally, and not through any canals or con- 
duits; and the sudden and very vivacious contraction must, 
one would think, rupture the surrounding soft material unless 
there were permanent minute porous tubes in it. On watching 
with the highest powers no displacement of the surrounding 
granules can be noticed after one of these active closings of the 
contractile vesicle ; but they sometimes precede a new move- 
ment in the general mass, such as the commencement of a 
streaming in a new direction, or the emission of a trans- 
parent lobose or sharp pseudopodium. In some instances the 
vesicle is moved along with the rest of the endosarc, and con- 
tracts and dilates in the midst, so that it is impossible that 
there can be any permanent outlet between it and the sur- 
rounding water. But when the vesicle is in its very common 
place, close to the food-entering end, there is sometimes an 
appearance as if there was a direct discharge through the dia- 
phane into the surrounding water. But I must confess that no 
motion occurs amongst the minutest particles which may sur- 
round the end of the Amoeba synchronously with the active con- 
traction of the vesicle. Corresponding vesicles occur in the Sun 
Animalcule which abounds in the water containing the Amoebae, 
and these occur on the very edge of the protoplasmic mass, 
bursting with such force as to shake the creature. The exit of 
their contents into the surrounding medium is visible enough, 
but this is not observed in Amoebae. 
Sometimes, when there are two contractile vesicles, they 
unite, and one large spot is produced which either assumes the 
spherical shape or remains irregular in outline until it contracts 
and disappears. Under all conditions, and whether the Amoeba 
is flourishing or dying from inanition and pressure, the con- 
tractile vesicle enlarges to its full size slowly in comparison 
with the sudden contraction, but the frequency of the pulsation, 
