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Part II: The Nature of the Forbidden
Fruit
Appendixes
1. The Origin of the Germ Cells
*
In the body
of the Paper the statement was made that cell differentiation
may possibly result from the progressive loss of some element
in the nucleus. Hamilton, Boyd, and Mossman stated that many
investigators of invertebrates and infra-mammalian invertebrates
have demonstrated conclusively an early segregation during development
of those cells which give rise to all the subsequent sex cells
of the organism: (39)
An early segregation of the
primordial germ cells has been described in mammals, but there
is still no generally accepted opinion on the time or site of
segregation of such cells or on their relationship to the definitive
germ cells. Several investigators have described primordial germ
cells in early human embryos and have suggested that they take
origin in the presomite stage (i.e., before body cells have formed).
Bradley M. Patten
in discussing the origin of the sex cells, said: (40)
For all vertebrates, including
man, there have been described in very young embryos certain
large cells in the yolk-sac that stand out in contrast with their
neighbors. This happens long before it is possible to tell whether
an embryo is to become male or female -- indeed, before any gonad
is laid down. These large cells have been identified by some
investigators as primordial sex cells and they believe that they
migrate from the yolk-sac entoderm to their final location in
the gonad. . . . The definitive germ cells, male or female,
are believed by some investigators to arise by successive mitotic
divisions from their primordial germ cells.
* This appendix will probably not be of interest
to most readers. It has to do with one aspect of this paper that
is fundamental and yet so involved that most people would not
want to be bothered with it. However, since it is fundamental,
it seemed desirable to deal with it very briefly and to provide
thereby references where the subject can be pursued further.
39. Hamilton, W. J., Boyd, J. D.; and Mossman, H. W., Human
Embryology, Williams and Wilkins, Baltimore, 1945,
p 204.
40. Patten, Bradley M., Human Embryology, Blakiston, Toronto,
1948, pp.13,14
 pg
1 of 3 
Olin
Nelsen believed that this view needs modification and that it
may be a progressive change in the character of the cytoplasm
of the germ cells that is the main factor which distinguishes
them from other body cells.
Nelsen gave some data bearing on
the point in time at which this cell differentiation begins to
take place: (41)
An early segregation of germinal
plasm (from which the subsequent germ cells or seed are derived)
is beyond argument. An actual demonstration to the continuity
of the germ plasm from generation to generation is found in
Ascarsis megalocephala described by Boveri in 1887. In this
form the chromatin of the somatic cells of the bodies undergoes
a dimunation and fragmenation, whereas the stem cells from which
the germ cells are ultimately segregated at the 16-cell to 32-cell
stage, retain the full complement of chromatin material. Thus
one cell of the 16-cell stage retains the intact chromosomes
and becomes the progenitor of the germ cells. The other 15 cells
will develop the somatic tissues of the body. The subsequent
diminution of the chromatin material in this particular species
has been shown to be dependent upon a certain cytoplasmic substance.
Nelsen further
remarked that:
The modern view of the germ
cell (germ plasm) embodies the concept that the germ cell is
composed of a nucleus as a carrier of the hereditary substance
of genes, and a peculiar specialized germinal cytoplasm. The
character of the cytoplasm of the germ cell is the main factor
distinguishing a germ cell from other some cells. . . .
41. Nelsen, Olin E., Comparative Embryology
of the Vertebrates, Blakiston, Toronto, 1953, pp.114ff.
pg.2
of 3
Olin
Nelsen believed that this view needs modification and that it
may be a progressive change in the character of the cytoplasm
of the germ cells that is the main factor which distinguishes
them from other body cells.
Nelsen gave some data bearing on
the point in time at which this cell differentiation begins to
take place: (41)
An early segregation of germinal
plasm (from which the subsequent germ cells or seed are derived)
is beyond argument. An actual demonstration to the continuity
of the germ plasm from generation to generation is found in
Ascarsis megalocephala described by Boveri in 1887. In this
form the chromatin of the somatic cells of the bodies undergoes
a dimunation and fragmenation, whereas the stem cells from which
the germ cells are ultimately segregated at the 16-cell to 32-cell
stage, retain the full complement of chromatin material. Thus
one cell of the 16-cell stage retains the intact chromosomes
and becomes the progenitor of the germ cells. The other 15 cells
will develop the somatic tissues of the body. The subsequent
diminution of the chromatin material in this particular species
has been shown to be dependent upon a certain cytoplasmic substance.
Nelson further
remarked that:
The modern view of the germ
cell (germ plasm) embodies the concept that the germ cell is
composed of a nucleus as a carrier of the hereditary substance
of genes, and a peculiar specialized germinal cytoplasm. The
character of the cytoplasm of the germ cell is the main factor
distinguishing a germ cell from other some cells. . . .
41. Nelsen, Olin E., Comparative Embryology
of the Vertebrates, Blakiston, Toronto, 1953, pp.114ff.
pg.3
of 3
Copyright © 1988 Evelyn White. All rights
reserved
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