VITELLINE MEMBRANE AND CORTICAL PARTICLES 263
species were used in these experiments. The impression is gained that the
treatment with the impure preparation was more efficient in removing
the block against cross-fertilization. This raises the interesting question
as to whether components other than proteins are relevant for the reception phenomenon. Périmâmes F antigen which has carbohydrate character could correspond to these components, whereas the C antigen could
be the trypsin-sensitive receptor. Extensive experimental work will here
be necessary.
Runnström (1952a, p. 54) expressed the view that a gradient of decreasing specificity prevails in the surface layers of the egg from the
outside to the interior of the egg. The sperm agglutination by egg water
(see Tyler, 1948) is more specific than the penetration of the sperm
through the vitelline membrane. The vitelline membrane, on the other
hand, is a carrier of a finer specificity than the cytoplasmic surface. This
implies that a series of consecutive reactions display themselves in the
fertilization process.
The further penetration of the sea urchin spermatozoon has not been
studied in sea urchins with the same accuracy as in the annelid Hydroides hexagonus and in the already mentioned enteropneust, Saccoglossus kowalevskii,
as described by Colwin and Col win (1961a,b,
1963a,b), who made a thorough electron-microscope investigation on the
matter. The scheme outlined by the Colwins is valid also for sea urchins.
The fusion of the egg plasma membrane with the sperm plasma membrane (Colwin and Colwin, loc. cit.) is a decisive step in the activation
process. Even if the penetration of the spermatozoon stops in this stage,
the cortical changes and a monaster formation take place. This follows,
for example, from experiments in which the eggs had been pretreated
with the oxidizing stain, porphyrindin, often resulting in prevention of
the engulfing of the spermatozoon (see Runnström, 1957; Runnström
et al. y 1959). As the Colwins state, a mixing of substances is possible
after the fusion of the plasma membranes of the gametes. From the site
of effective sperm attachment, an impulse propagates until it has covered
the whole egg surface. In this context it may be stated only that the
plasma membrane is involved in the propagation of this impulse. The
propagation is initiated by the fusion of the plasma membranes of two
gametes, which results in about 30,000 fusions between plasma membrane and the membranes of cortical particles. The fusion between the
plasma membrane of the gametes is directed from outside to inside,
whereas the fusion between the cortical particles and the plasma membrane is directed from inside to outside. Nevertheless, the two processes
must be closely related. In both cases fusion of unit membranes are involved. This writer regards the fertilization as a multistep process in
species were used in these experiments. The impression is gained that the
treatment with the impure preparation was more efficient in removing
the block against cross-fertilization. This raises the interesting question
as to whether components other than proteins are relevant for the reception phenomenon. Périmâmes F antigen which has carbohydrate character could correspond to these components, whereas the C antigen could
be the trypsin-sensitive receptor. Extensive experimental work will here
be necessary.
Runnström (1952a, p. 54) expressed the view that a gradient of decreasing specificity prevails in the surface layers of the egg from the
outside to the interior of the egg. The sperm agglutination by egg water
(see Tyler, 1948) is more specific than the penetration of the sperm
through the vitelline membrane. The vitelline membrane, on the other
hand, is a carrier of a finer specificity than the cytoplasmic surface. This
implies that a series of consecutive reactions display themselves in the
fertilization process.
The further penetration of the sea urchin spermatozoon has not been
studied in sea urchins with the same accuracy as in the annelid Hydroides hexagonus and in the already mentioned enteropneust, Saccoglossus kowalevskii,
as described by Colwin and Col win (1961a,b,
1963a,b), who made a thorough electron-microscope investigation on the
matter. The scheme outlined by the Colwins is valid also for sea urchins.
The fusion of the egg plasma membrane with the sperm plasma membrane (Colwin and Colwin, loc. cit.) is a decisive step in the activation
process. Even if the penetration of the spermatozoon stops in this stage,
the cortical changes and a monaster formation take place. This follows,
for example, from experiments in which the eggs had been pretreated
with the oxidizing stain, porphyrindin, often resulting in prevention of
the engulfing of the spermatozoon (see Runnström, 1957; Runnström
et al. y 1959). As the Colwins state, a mixing of substances is possible
after the fusion of the plasma membranes of the gametes. From the site
of effective sperm attachment, an impulse propagates until it has covered
the whole egg surface. In this context it may be stated only that the
plasma membrane is involved in the propagation of this impulse. The
propagation is initiated by the fusion of the plasma membranes of two
gametes, which results in about 30,000 fusions between plasma membrane and the membranes of cortical particles. The fusion between the
plasma membrane of the gametes is directed from outside to inside,
whereas the fusion between the cortical particles and the plasma membrane is directed from inside to outside. Nevertheless, the two processes
must be closely related. In both cases fusion of unit membranes are involved. This writer regards the fertilization as a multistep process in