22, BRITISH FRESHWATER RHIZOPODA. 
REPRODUCTION. 
Several modes of reproduction have heen observed 
among the Rhizopoda, but, from the infrequency of 
their occurrence, some have not been satisfactorily 
worked out. The modes most frequently noticed are— 
(1) simple fission or binary self-division; and (2) spore- 
formation. The latter is little more than the breaking 
up of the plasma into fragments, and the development 
of these; each separate portion being the germ, or 
earhest stage in the existence, of a new individual. 
This process is usually preceded by the encistment of 
the adult individual ; that is to say, the formation, upon 
the withdrawal of the plasma into the interior of the 
test (in the Conchulina) of a spherical or oval cist, 
which acquires a hard (chitinous or possibly siliceous) 
coat. The cist remains quiescent for a longer or 
shorter period, until division of the plasma and nucleus 
takes place, and the “spores” are liberated. Fre- 
quently —but, according to Ray Lankester, not neces- 
sarily—two (rarely three or more) individuals come 
together and fuse before breaking up into spores. 
This process is known as “conjugation”; and there 
can be no doubt, says the same authority, that the 
physiological significance of the process is similar to 
that of sexual fertilization, namely, that the new spores 
are not merely fragments of an old individual, but are 
something totally new, as they consist of the substance 
of individuals which previously had different. life- 
experiences. Whilst spore-formation is not necessarily 
preceded by conjugation, conjugation is not necessarily 
followed by spore-formation. Professor Lankester 
further remarks: “There is certainly no marked line 
to be drawn between reproduction by simple fission, 
and reproduction by spore-formation ; both are a more 
or less complete dividing of the parent protoplasm into 
separate masses; whether the products of the first 
fission are allowed to nourish themselves and grow 
