THE ACRASINA
127
characters, in my cultures, though such cells may have all these characters, except heavy granulation (see Section II, A, 3), they may show
only some of them, in almost any combination, or even none at all.
The relation of I-cells to centres. Ennis and Sussman reported that the
occurrence of the aggregation centres was almost perfectly correlated
with the presence of I-cells in the population and even with their actual
position. The first sign of aggregation they saw was cell clumping. This
began around or in the immediate vicinity of an I-cell and spread concentrically outwards. The outer clumps then elongated and moved as
aggregation streams directly towards the one surrounding the I-cell, or
in some cases towards an abnormally large clump very near it—
practically always less than 200 μ away.
Comment. This description was illustrated by a single series of timelapse photographs (Sussman, 1958; Sussman and Ennis, 1959), which
was supposed to show a centre forming at the actual site of an I-cell.
Of course, even if a large cell is not specifically involved in starting a
centre, there must be cases in which one happens to be present. But the
published photographs did not in fact show such a case. The centre
actually developed within a group of clumps first visible when the I-cell
was 400-500 μ away, and the I-cell clump was no more than 100 μ nearer
in the last photograph in which it could be arrowed. The definite centre
visible in the next photograph appeared to have developed at the I-cell's
position only because the field had been shifted. It is of interest that the
centre did not form within an equally large system of clumps that was
appreciably nearer the I-cell. Thus, the authors not only did not photograph what they supposed, but accidentally recorded what was said
almost never to happen. The same photographs do not seem to support
the description of concentric clumping: clumps appear at the same time
in irregular groups scattered over the entire visible field, those at the
edge being about 700 μ from the I-cell; and indeed if the I-cell were not
arrowed, it would be impossible to guess its position. Moreover, a still
earlier stage of aggregation has been described, in which the cells condense into clouds (Shaffer, 1959; Section IV, B, 2); the Sussman photographs show that this stage had already been reached when the field
was selected because it contained an I-cell, for there were then about
500 cells in a square millimetre, though initially the average was 200.
If the large cells behaved just like the others, there must therefore have
been a greater chance of finding them in areas that subsequently produced definite centres.
Konijn and Raper (1961) and Gerisch (1961a) found that the aggregation of small populations of haploid NC4, whether centrifuged or not,
was not dependent on the presence of cells in the I-cell size range.
And I have found this to be true of isolated populations of 20-100
127
characters, in my cultures, though such cells may have all these characters, except heavy granulation (see Section II, A, 3), they may show
only some of them, in almost any combination, or even none at all.
The relation of I-cells to centres. Ennis and Sussman reported that the
occurrence of the aggregation centres was almost perfectly correlated
with the presence of I-cells in the population and even with their actual
position. The first sign of aggregation they saw was cell clumping. This
began around or in the immediate vicinity of an I-cell and spread concentrically outwards. The outer clumps then elongated and moved as
aggregation streams directly towards the one surrounding the I-cell, or
in some cases towards an abnormally large clump very near it—
practically always less than 200 μ away.
Comment. This description was illustrated by a single series of timelapse photographs (Sussman, 1958; Sussman and Ennis, 1959), which
was supposed to show a centre forming at the actual site of an I-cell.
Of course, even if a large cell is not specifically involved in starting a
centre, there must be cases in which one happens to be present. But the
published photographs did not in fact show such a case. The centre
actually developed within a group of clumps first visible when the I-cell
was 400-500 μ away, and the I-cell clump was no more than 100 μ nearer
in the last photograph in which it could be arrowed. The definite centre
visible in the next photograph appeared to have developed at the I-cell's
position only because the field had been shifted. It is of interest that the
centre did not form within an equally large system of clumps that was
appreciably nearer the I-cell. Thus, the authors not only did not photograph what they supposed, but accidentally recorded what was said
almost never to happen. The same photographs do not seem to support
the description of concentric clumping: clumps appear at the same time
in irregular groups scattered over the entire visible field, those at the
edge being about 700 μ from the I-cell; and indeed if the I-cell were not
arrowed, it would be impossible to guess its position. Moreover, a still
earlier stage of aggregation has been described, in which the cells condense into clouds (Shaffer, 1959; Section IV, B, 2); the Sussman photographs show that this stage had already been reached when the field
was selected because it contained an I-cell, for there were then about
500 cells in a square millimetre, though initially the average was 200.
If the large cells behaved just like the others, there must therefore have
been a greater chance of finding them in areas that subsequently produced definite centres.
Konijn and Raper (1961) and Gerisch (1961a) found that the aggregation of small populations of haploid NC4, whether centrifuged or not,
was not dependent on the presence of cells in the I-cell size range.
And I have found this to be true of isolated populations of 20-100