4. C E L L T Y P E S
147
macrophages, leucocytes, and the microglia. On the other hand, the
fibroblasts derived from the various tissues mentioned, when given the
opportunity to behave more as they would in the body, can often reassume their own original characters, but cannot, or do not easily,
assume those of other cells, either from the same group or from other
groups. Differentiation in the embryo has left its mark on the cells of
the developing and adult organism, so that although some return or
adaptation to a more generalized and embryonic form may be possible,
differentiated somatic cells tend in culture to maintain some at least
of their specific qualities, though it may be in a latent form.
There are, of course, some types of cells, like the red and white blood
cells, which do not survive for long in vitro and these obvious examples
raise the question as to how many other types of cells, more deeply
integrated into the tissues of the body, or less easily recognized in
culture, suffer a similar fate when their containing tissues are explanted
in vitro.
I I I .
T H E M A I N C E L L T Y P E S
Study of the cells growing out from tissues on to a flat surface, such as
agar, plasma or glass, reveals about five or six main types of cellular
behaviour. These have been discussed in detail elsewhere (Willmer,
1960) but their main features may be summarized as follows:
(a) Epitheliocytes, from the covering layers of a wide variety of ectodermal, endodermal and mesodermal tissues, emerge as sheets of cells
closely adherent to each other. They probably derive from cells which
were originally on the external surface of the body, where external
surface includes the lining of the alimentary canal and its offshoots and
also the lining of the urinogenital system.
(b) Mechanocytes (fibroblasts) again from a wide variety of sources, all
of which are, however, mesenchymal, emerge as a loose network of
cells, in which the cells are polarized and partly contiguous. They may
sometimes grow in the form of sheets, when derived from endothelia
and mesothelia.
(c) Amoebocytes, derived from monocytes in the blood, from the macrophages in practically every tissue and from the microglia, show much
more random movement, and these cells remain isolated from each
other. These also may, however, under some conditions produce
loosely knit sheets of cells. They also have a tendency to aggregate
into giant cells.
(d) Nerve cells send out long and sometimes elaborate processes, but
their cell bodies may hardly move at all, although long-term cultures
147
macrophages, leucocytes, and the microglia. On the other hand, the
fibroblasts derived from the various tissues mentioned, when given the
opportunity to behave more as they would in the body, can often reassume their own original characters, but cannot, or do not easily,
assume those of other cells, either from the same group or from other
groups. Differentiation in the embryo has left its mark on the cells of
the developing and adult organism, so that although some return or
adaptation to a more generalized and embryonic form may be possible,
differentiated somatic cells tend in culture to maintain some at least
of their specific qualities, though it may be in a latent form.
There are, of course, some types of cells, like the red and white blood
cells, which do not survive for long in vitro and these obvious examples
raise the question as to how many other types of cells, more deeply
integrated into the tissues of the body, or less easily recognized in
culture, suffer a similar fate when their containing tissues are explanted
in vitro.
I I I .
T H E M A I N C E L L T Y P E S
Study of the cells growing out from tissues on to a flat surface, such as
agar, plasma or glass, reveals about five or six main types of cellular
behaviour. These have been discussed in detail elsewhere (Willmer,
1960) but their main features may be summarized as follows:
(a) Epitheliocytes, from the covering layers of a wide variety of ectodermal, endodermal and mesodermal tissues, emerge as sheets of cells
closely adherent to each other. They probably derive from cells which
were originally on the external surface of the body, where external
surface includes the lining of the alimentary canal and its offshoots and
also the lining of the urinogenital system.
(b) Mechanocytes (fibroblasts) again from a wide variety of sources, all
of which are, however, mesenchymal, emerge as a loose network of
cells, in which the cells are polarized and partly contiguous. They may
sometimes grow in the form of sheets, when derived from endothelia
and mesothelia.
(c) Amoebocytes, derived from monocytes in the blood, from the macrophages in practically every tissue and from the microglia, show much
more random movement, and these cells remain isolated from each
other. These also may, however, under some conditions produce
loosely knit sheets of cells. They also have a tendency to aggregate
into giant cells.
(d) Nerve cells send out long and sometimes elaborate processes, but
their cell bodies may hardly move at all, although long-term cultures