GENERAL ANATOMY. 19 
GENERAL ANATOMY. 
Although in every respect a continuous structure, the body is 
differentiated into a large number of parts, or organs, the latter 
being more or less individual in form, composition, or function. 
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. 
also a minute spherical body, 
the nucleolus. The chief features of a typical cell are illustrated 
in the accompanying figure (1) of the developing ovum, the latter 
being a single cell, noteworthy for its large size, and also one in 
which the external form is not greatly modified, as it is in the 
majority of the cells of the body. Its enclosing membrane, the 
zona pellucida, by which in its natural position in the ovary it is 
separated from the surrounding follicular cells, is considered to 
belong in part to the latter. 
As fundamental living matter, protoplasm possesses certain 
properties on which the functions of the body ultimately depend. 
