92 PROTOZOA. 
of a micro-nucleus. These. fragments are each one-fourth 
part of the original overgrown micro-nucleus. 
(2) In each individual one of the parts moves across 
into the other individual and fuses with the remaining part 
of that individual. Sometimes the migrating parts are 
termed the male pronuclei, and the other two the female 
pronuclet, 
(3) Soon after this communication between the two 
individuals becomes interrupted and they part. -In the 
meanwhile the single-fused nucleus in each divides into two 
and then into four, so that each individual has then four 
nuclei. 
(4) Two quarters pass to each end of the animal and 
binary fission takes place. One quarter grows into a macro- 
nucleus and the other remains a micro-nucleus. The result 
is a pair of offspring with a macro-nucleus and a micro- 
nucleus each 
This account should be carefully compared with the 
remarks in Chapter V. It will then be seen that the 
presence of two kinds of nuclei is the principal factor 
causing complication. 
Paramecium isa type of the Sub-kingdom PROTOZOA, 
for it is a single cell with all the vital activities confined 
therein. It is a type of the phylum CORTICATA, for it 
has a definite shape of the body due to a limiting cortex ; 
this involves the important feature of a definite mouth. 
In the CORTICATA it belongs to the class Citiata for 
its locomotive organs are in the form of cilia. The cilia 
are evenly distributed over the surface of the body, and 
hence it is a member of the order Holotricha. 
III.—VORTICELLA. 
Vortzcella is a small freshwater and marine animal closely allied to 
the last type, from which it chiefly differs in being sedentary or fixed. 
It may affix itself to almost any foreign body, living or non-living. The 
body of the animal is bell-shaped with a long stalk. Asin Paramecium 
there is a cuticle and cortex. The cilia are confined to the rim of 
the bell and produce vortex-currents by which food-particles are 
brought to the mouth. The thickened ciliated rim is called the fer?- 
stome, and immediately inside there runs a circular groove leading 
down at one part into a funnel-shaped vestébu/e. The base of the 
