Organs are arranged for the most part in systems, each of which is
concerned with some general or fundamental function, to which
several organs may contribute.
In a more general way the body may be considered as an
assemblage of tissues. The latter are layers or aggregations of
similarly differentiated cells. They are of several different kinds
and are variously associated.in the formation of organs. Being
structures of an intermediate position they may be considered either
as organ components or as products of specialized cells.
As a body-unit a cell
consists of a small mass of
living protoplasm, contain- a Hie fe.
ing a central body, the nuc- Kant

leus, and surrounded or en- S/

closed on its free border by ok

a cell-membrane. The = beste
nucleus is a highly organized = |: 2,
body, having an important s"

function in the reproduction L chr.
of the cell and also in its Ors =~
if aA)

general activity or metabol- OTT
ism. It contains a charac-

oa Fic. 1. Developing ovum of the_ rabbit.
teristic formed material, From a section of the ovary: chr., chromatin;

‘ n.m., nuclear membrane; p.f., cells of the primary
chromatin, and frequently ovarian follicle; z.p., zona pellucida; pr., proto-
. : plasm.
