558 
SEXUAL GENERATION :—SPERM-CELLS. 
preceding in exactly tlie same manner as the flowering and 
fruiting of Plants differ from their extension and propagation 
hy leaf-buds.—In all save the very lowest tribes of Animals, 
we meet at particular seasons with two peculiar sets of cells, 
termed sperm-cells and germ-cells; these are sometimes borne 
by the same individuals, which then correspond as regards 
their reproductive apparatus with the generality of Plowering 
Plants ; but they are more commonly separated, as in dioecious 
Plants (Veget. Physiol., § 409); the individual bearing the 
“ sperm-cells ” being then designated as the male , and the 
individual bearing the “ germ-cells” as the female. 
731. The“ sperm-cells” very closely resemble those con¬ 
tained within the antheridia of Cryptogamia (Veget. Physiol. 
§ 399 ; Botany, §§ 737, 776). When mature, each cell is 
found to contain one or more spirally 
coiled filaments (fig. 301), which, 
when set free by the bursting of 
the cell, have an active spontaneous 
movement lasting for some time like 
ciliary action. These filaments were 
formerly regarded as true Animal¬ 
cules ; but since other examples of 
independent movement have been 
discovered in what are certainly 
nothing else than detached parts of 
the organism, and more especially 
since moving filaments of a precisely 
analogous character have been dis¬ 
covered in Plants, all idea of their 
independent animality has been laid 
aside, and they are now known as 
spermatozoids .—The use of their 
motor activity is obviously to bring 
Fig. 301.— Spermatozoids : 
. e, immature spermacetis. 
them into contact with the germ-cells, when both have been 
set free from the interior of the bodies within which they 
were formed. When the sperm-cells are developed in a 
special or distinct organ, as happens in all save the lowest 
types of Animal structure, this organ usually more or less 
resembles the ordinary glands in structure (§§ 356, 357), and 
is termed the Testis. 
732. The “germ-cells” are not so clearly distinguished 
