PARAMGCIUM. gt 
surface there slopes backwards a shallow cone-shaped 
depression, the vestébule. It is lined by 
special cilia, which cause food-currents. At 
its base or inner end is an opening into the inner fluid 
protoplasm, which is the permanent mouth or ingestive 
aperture. Food-particles, usually microscopic algee, are 
driven by the ingestive cilia down the vestibule and 
through the mouth into the interior of the body. Here 
they are then digested. and their residua are egested, 
but they appear to follow a definite course within the 
organism, first towards the posterior end, then forwards 
dorsally and backwards along the ventral surface, to 
be eventually extruded or egested at a special spot just 
behind the mouth. There appears to be no permanent 
opening or anus, but the temporary anus is always formed 
at the same spot. 
Under the dorsal surface and lying towards the anterior 
and posterior ends of the animal there are two contractile 
vacuoles which do not differ essentially from the single one 
found in Ameba. About the centre of the animal there lies 
a large oval macro-nucleus. in close contact with which 
there is a small mzcro-nucleus, 
There are no definite organs of respiration, sense-organs, 
nor nervous system. ‘ 
Growth in Paramecium is succeeded by binary fission 
into two equal parts by an oblique division, but sooner or 
later the process of conjugation must intervene in order 
that life may be maintained. 
We have already dealt with the general phenomenon of 
conjugation (see Chapter V.). Paramecium proceeds 
normally in conjugation. During this pro- 
cess two individuals are in close contact 
along their ventral surface, their protoplasm becoming 
continuous through their mouths. The essential changes 
are as follows :— 
(1) In each individual the macro-nucleus breaks up 
and disintegrates, to be thrown out or absorbed, and 
the micro-nucleus grows rapidly and then divides by 
two rapid divisions into four, two of these pieces being 
absorbed. Thus by these processes the macro-nucleus 
and micro-nucleus are now reduced to two fragments 
Alimentative, 
Conjugation. 
