eee ee 
558 SEXUAL GENERATION :—SPERM-CELLS. 
preceding in exactly the same manner as the flowering and 
fruiting of Plants differ from their extension and propagation — 
by leaf-buds.—In all save the very lowest tribes of Animals, — 
we meet at particular seasons with two peculiar sets of cel 
termed sperm-cells and germ-cells ; these are sometimes bor 
by the same individuals, which then correspond as regards 
their reproductive apparatus with the generality of Flowermg 
Plants ; but they are more commonly separated, as in diecious 
Plants (Vecrr. Puystox., § 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 (Vecrr. PHysiob. 
§ 399; Borany, §$ 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 © 
(pleat alate Ue, aside, and they are now known as 
immature spermeelis.  $permatozoids—The use of their 
motor activity is obviously to bring 
them into contact with the germ-cells, when both have been 
set free from the interior of the bodies within which they 
were formed. When the sperm-cells are developed in a 
special or distinct organ, as happens in all save the lowest 
types of Animal structure, this organ usually more or less 
resembles the ordinary glands in structure ($§ 356, 357), and 
is termed the Testis, pot 
732, The “germ-cells” are not so clearly distinguished 
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