234 NATURAL SCIENCE [October 
fish.t Since then we have learned that the ultimate units of 
structure of the familiar organisms are identical in character with 
the entire organism of one of such microscopic being; and the 
search we have referred to would be now regarded as equivalent to 
seeking in a limestone pebble the pillars and buttresses, the vaults 
and domes of a great cathedral in miniature. Such units of struc- 
ture are called ‘cells, an ill-chosen term indeed, whose signification, 
however, as a nucleated unit of protoplasm, is familiar to everyone. 
The lower organisms consist of single cells or of aggregates of 
similar cells ; the higher ones consist of complicated arrangements of 
those dissimilar aggregates of cells which we call tissues. The 
former we call Protists, distinguishing between Protozoa and Proto- 
phytes according as the mode of existence is animal or plant-like ; 
the higher animals and plants we term Metazoa and Metaphytes 
respectively, the appropriate conjoint term, ‘ Metists, not having 
been coined by any recognised authority. 
Throughout the higher groups the act of reproduction? of the 
race consists in the separation from the complex organism of single 
reproductive cells, which may either independently grow up into the 
original form, or else one with another fuse to produce a new cell 
which grows up. Again in most Plants and many Animals multi- 
cellular portions of the body may become detached, and finally develop 
into complete organisms ; this we shall call ‘ propagation, not ‘ repro- 
duction. In either case the parent body continues to exist, alive or 
dead, after the detachment of these cells or groups of cells. In Protists, 
matters are very different; for here, when the cell individual has 
attained its full size, it usually divides into two new cells, and itself 
is no more, alive or dead. We call the original cell a ‘mother cell,’ 
the new ones ‘daughter-cells, by a convenient metaphor; but we 
must remember that the devoted mother here absolutely merges her 
very existence into that of her offspring, a self-denying type of 
maternity often imagined but never realised among ourselves. Thus 
as Weismann first explicitly stated, the Protists may escape personal 
death by the sacrifice of their individual life; he therefore terms 
them ‘immortal. It is with cellular pedigree, according to 
the mode of parentage we have just explained, that we shall mostly 
have to deal in this paper. 
The modes of reproduction among Protists are many and various. 
*Thus Baker writes in the middle of the last century: ‘‘ Search we further and 
examine the Animalcules—many Sorts whereof it would be impossible for an human Eye 
unassisted to discern ; those breathing Atoms, so small they are almost all Workman- 
ship! in them too we shall discover the same Organs of Body, Multiplicity of Parts, 
Variety of Motions, Diversity of Figures, and Particular Ways of Living as in the 
larger Animals.—How amazingly curious must the Internal Structure of these Creatures 
be! The Heart, the Stomach, the Entrails and the Brain. How minute and fine the 
Bones, Joints, Muscles and Tendons! How exquisitely delicate beyond all Conception 
the Arteries, Veins and Nerves!” (‘‘The Microscope Made Easy,” by Henry Baker, 
ed. v., 1767.) 
* In the limited sense, distinguished from ‘ propagation,’ as defined immediately. 
