28 ZOOLOGY 
as in Paramoecium, and fission is oblique. Recent observation 
on this and other forms shows that as long as the products of 
artificial division contain part of the nucleus with its chromatin, 
they are capable of regenerating the lost parts; those portions 
of the body which are without any portions of the nucleus die. 
Lalantidium is a genus which lives parasitically in the 
human colon, and with Jyctotherus, is found in the rectum 
of Anura, ete. The latter is interesting, since it 1s provided 
with a permanent anus with a cuticular lining. In most Cihata 
the situation of the cell anus is constant, but there is nothing 
to indicate its position, except when waste matter is being 
expelled. 
Order III. Holotricha.—Jn this order the body is uni- 
formly clothed with short cilia, arranged in regular rows. Some- 
times those on the adoral surface are slightly longer than the 
others. 
Paramoecium is one of the commonest genera of this 
order. Close underneath its cuticle in the ectosarc, is a layer 
of oval bodies, the Zvrichoeysts; these, when the animal is 
irritated, discharge threads, which have probably the same 
functions as the stinging threads in the nematocysts of 
Coelenterata. 
Maupas has recently described the conjugation of Para- 
moecium aurelia, which takes place as follows. As soon as two 
individuals come together, the paranuclei, of which there are 
two (Fig. 21, 1), separate themselves from the nucleus, increase 
in size (Fig. 22, A), become spindle-shaped, and ultimately divide 
into two (2 and B). The two halves of each divide again (C), so 
that a stage is found with eight similar portions of the original 
paranucleus: in each individual (3 and 4). Of these eight 
corpuscles, seven are absorbed and disappear (5); the eighth 
alone, and this is always that one which lies nearest to the 
mouth, undergoes further change. This corpuscle increases 
in size and divides into two (6 and D), thus giving rise to the 
male and the female pronucleus. The former of these passes out 
of each conjugating individual into the other, and there fuses 
with the female pronucleus (7 and E). The conjugating animals 
now separate. The “ fertilised” paranucleus now divides into 
