148
E . N. W I L L M E R
demonstrate that they are in fact capable of some migration. Sympathetic ganglion cells, on the other hand, are more motile than neurones
of the CNS, and they have been seen to emerge from cultures of adult
human ganglia and even to divide in culture (Murray and Stout, 1947).
(e) Neuroglia cells (excluding the microglia) emerge either as bipolar
oligodendrocytes with membranous pseudopodia at each end, or as
astrocytes which typically have large lamelliform membranes. Similarly, Schwann cells may emerge as rather characteristically spindleshaped cells (Abercrombie and Johnson, 1942) or as cells appearing
more like amoebocytes (macrophages) (Weiss, 1944). By comparison
with other cells, nerve cells and neuroglia cells from different parts of the
nervous system have been rather inadequately studied.
(f) Lymphocytes on a flat surface show either the "hand-mirror" type
of gliding movement (so-called because the shape of the cell when it is
on the move resembles an oval hand-mirror with the handle pointing
backward), or they round up and only produce filiform pseudopodia.
The gliding movement is oriented, and the cell essentially progresses
by a wave of constriction passing posteriorly and forcing the contents
of the "handle of the mirror" forwards. Lymphocytes, like all the
other types of blood cells except the monocytes, only survive for a few
hours or days in vitro and then disintegrate (see Vol. 2, Chapter 2).
I V . T H E S I G N I F I C A N C E OF T H E M A I N C E L L T Y P E S
The extent of the simplification undergone by cells from different
sources, into these few types when they emerge from such cultures as
encourage unorganized growth is partly dependent on time. For
example, heart-muscle cells may be distinguishable as such for a time,
i.e. a few days or weeks at the most; but they appear gradually to
transform to generalized mechanocytes. Some forms of ciliated epithelial cells, e.g. in the olfactory epithelium, may retain their cilia for
a time (Rose, Pomerat and Danes, 1949), but most epithelia rather
quickly form an apparently uniform pavement of cells.
It is pertinent and of fundamental importance to enquire into the
significance of this limited number of forms of movement and behaviour.
The type of behaviour is probably partly intrinsic in the cells themselves since all the types of cell mentioned can, at least for a time, exist
quite happily side by side in the same medium (Fig. 1). Moreover,
cells from each of the various tissues always tend to assume the form
which is characteristic of that tissue; e.g. in cultures of the skin, epidermal
cells produce sheets, but dermal cells emerge as mechanocytes and
amoebocytes. The cell forms are also partly extrinsic, as is made evident
E . N. W I L L M E R
demonstrate that they are in fact capable of some migration. Sympathetic ganglion cells, on the other hand, are more motile than neurones
of the CNS, and they have been seen to emerge from cultures of adult
human ganglia and even to divide in culture (Murray and Stout, 1947).
(e) Neuroglia cells (excluding the microglia) emerge either as bipolar
oligodendrocytes with membranous pseudopodia at each end, or as
astrocytes which typically have large lamelliform membranes. Similarly, Schwann cells may emerge as rather characteristically spindleshaped cells (Abercrombie and Johnson, 1942) or as cells appearing
more like amoebocytes (macrophages) (Weiss, 1944). By comparison
with other cells, nerve cells and neuroglia cells from different parts of the
nervous system have been rather inadequately studied.
(f) Lymphocytes on a flat surface show either the "hand-mirror" type
of gliding movement (so-called because the shape of the cell when it is
on the move resembles an oval hand-mirror with the handle pointing
backward), or they round up and only produce filiform pseudopodia.
The gliding movement is oriented, and the cell essentially progresses
by a wave of constriction passing posteriorly and forcing the contents
of the "handle of the mirror" forwards. Lymphocytes, like all the
other types of blood cells except the monocytes, only survive for a few
hours or days in vitro and then disintegrate (see Vol. 2, Chapter 2).
I V . T H E S I G N I F I C A N C E OF T H E M A I N C E L L T Y P E S
The extent of the simplification undergone by cells from different
sources, into these few types when they emerge from such cultures as
encourage unorganized growth is partly dependent on time. For
example, heart-muscle cells may be distinguishable as such for a time,
i.e. a few days or weeks at the most; but they appear gradually to
transform to generalized mechanocytes. Some forms of ciliated epithelial cells, e.g. in the olfactory epithelium, may retain their cilia for
a time (Rose, Pomerat and Danes, 1949), but most epithelia rather
quickly form an apparently uniform pavement of cells.
It is pertinent and of fundamental importance to enquire into the
significance of this limited number of forms of movement and behaviour.
The type of behaviour is probably partly intrinsic in the cells themselves since all the types of cell mentioned can, at least for a time, exist
quite happily side by side in the same medium (Fig. 1). Moreover,
cells from each of the various tissues always tend to assume the form
which is characteristic of that tissue; e.g. in cultures of the skin, epidermal
cells produce sheets, but dermal cells emerge as mechanocytes and
amoebocytes. The cell forms are also partly extrinsic, as is made evident