582
E T I E N N E W O L F F
morphism might be caused by a different mechanism like some of
those known amongst insects, as for example the loss of, or absence of
the division of, an X chromosome in the course of one of the early
mitoses of segmentation.
These deductions go further than the, as yet, fragmentary results
listed in the author's brief publication. In conclusion, it is worthwhile
to stress the extraordinary faculty for the regulation of excess material
manifested by mammalian eggs; a faculty which is the counterpart of
the remarkable regulation of deficiences.
Tarkowski has shown decisively that two mammalian eggs can unite
to form a single individual. His arguments in proof of this thesis are as
follows: (1) in vitro observation of the development of fused eggs to the
blastocyst stage; (2) the presence of bipartite hermaphroditism when
individuals of opposite sexes are fused together; (3) the fact that when
two eggs of different type are combined, fifteen out of fifteen young
show the eye pigmentation of the hybrid type. This fact does not represent a decisive proof, but it is a serious argument, and for this reason:
it is rather improbable that, if one of the eggs is being eliminated from
the combination, it is the non-pigmented LAB Grey one which is
being eliminated every time.
I V . C U L T U R E IN VITRO
OF T H E E M B R Y O S OF F I S H A N D
R E P T I L E S
In contrast to the embryos of amphibians, birds and Mammalia,
which have been the objects of many important researches, only a
limited amount of work has been done on the blastoderms of fish and
reptiles.
Fish. Oppenheimer (1936) carried out experiments with culture
in vitro in an attempt to eliminate the yolk from the egg of Fundulus
heteroclitus at different stages of segmentation. The blastoderms were
then raised in a Holtfreter solution of twice the normal strength. When
removed before stage 32, they gave no differentiation at all and became
transformed into large ectodermic vesicles which the author called
hyperblastulae. After stage 32, the blastoderms gastrulated and gave
rise to embryonic formations. These were in general very disordered
and more significant in the cephalic region than in the truncal region.
The absence of differentiation in blastoderms isolated before stage 32
is due very likely to a considerable loss of periblast-tissue of the marginal
zone which may have an important function in organization. As to
the generally defective organization of older blastoderms, it may be
explained by the absence of yolk which, though not indispensable to
E T I E N N E W O L F F
morphism might be caused by a different mechanism like some of
those known amongst insects, as for example the loss of, or absence of
the division of, an X chromosome in the course of one of the early
mitoses of segmentation.
These deductions go further than the, as yet, fragmentary results
listed in the author's brief publication. In conclusion, it is worthwhile
to stress the extraordinary faculty for the regulation of excess material
manifested by mammalian eggs; a faculty which is the counterpart of
the remarkable regulation of deficiences.
Tarkowski has shown decisively that two mammalian eggs can unite
to form a single individual. His arguments in proof of this thesis are as
follows: (1) in vitro observation of the development of fused eggs to the
blastocyst stage; (2) the presence of bipartite hermaphroditism when
individuals of opposite sexes are fused together; (3) the fact that when
two eggs of different type are combined, fifteen out of fifteen young
show the eye pigmentation of the hybrid type. This fact does not represent a decisive proof, but it is a serious argument, and for this reason:
it is rather improbable that, if one of the eggs is being eliminated from
the combination, it is the non-pigmented LAB Grey one which is
being eliminated every time.
I V . C U L T U R E IN VITRO
OF T H E E M B R Y O S OF F I S H A N D
R E P T I L E S
In contrast to the embryos of amphibians, birds and Mammalia,
which have been the objects of many important researches, only a
limited amount of work has been done on the blastoderms of fish and
reptiles.
Fish. Oppenheimer (1936) carried out experiments with culture
in vitro in an attempt to eliminate the yolk from the egg of Fundulus
heteroclitus at different stages of segmentation. The blastoderms were
then raised in a Holtfreter solution of twice the normal strength. When
removed before stage 32, they gave no differentiation at all and became
transformed into large ectodermic vesicles which the author called
hyperblastulae. After stage 32, the blastoderms gastrulated and gave
rise to embryonic formations. These were in general very disordered
and more significant in the cephalic region than in the truncal region.
The absence of differentiation in blastoderms isolated before stage 32
is due very likely to a considerable loss of periblast-tissue of the marginal
zone which may have an important function in organization. As to
the generally defective organization of older blastoderms, it may be
explained by the absence of yolk which, though not indispensable to