262
JOHN RUNNSTRÖM
of Arbacia lixula (Hultin, 1948b). Addition of egg water from Arbacia
eggs, however, enhanced the cross-fertilization with sperm from Arbacia
when the vitelline membrane was removed. Addition of rabbit serum,
bovine albumin, or glycine had the same effect as egg water (see also,
Runnström, 1952a, p. 72; Hagström, 1956b). It is obvious, therefore,
that unspecific factors—primarily increasing the motility of the spermatozoa—may manifest the protecting effect of the vitelline membrane.
The results from the crosses in which Arbacia sperm were used, thus, do
not invalidate Hultin's conclusion regarding the role of the vitelline membrane. It seems very likely that the vitelline membrane has a specific
structure that makes it a reception site for the spermatozoa. Moreover, it
protects the egg against cross-fertilization, but, as Hagström (1959)
pointed out, deeper layers of the egg surface may take part in this protection (see further Section II,F). Hagström's data show quantitatively
that the rate of fertilization is lower in cross-fertilization between different genera than in homologous fertilization, even if almost 100% fertilization will eventually be attained in the former, as, for example, in
the cross between Psammechinus
female and Paracentrotus
male. In the
case presented in Hagström's Fig. 2 (1959), the cross-fertilization had a
50% fertilization value of about 80 sec, whereas the corresponding value
was 20 sec in the homologous fertilization. The acrosomal region of the
spermatozoon of Paracentrotus
does not fit as well to the dominating
egg receptor as that of the homologous spermatozoon. Nevertheless, there
is a certain degree of fitness which gives a measurable rate of fertilization. In other crosses, for example, between Sphaerechinus
female and
Paracentrotus
male, the rate of fertilization was very low (50% fertilization not being attained in 2-3 hr) ; following a pretreatment with
0.001% trypsin for 10 min, the rate of cross-fertilization increased to
about the rate found in homologous fertilization after trypsin pretreatment of the eggs (Hagström, loc. cit., Figs. 3 and 4). After removal of
the species-specific receptors by trypsin pretreatment, both homologous
and heterologous sperm are almost in the same situation when attacking
the egg surface. The acrosome of homologous spermatozoon does not
meet the rate increasing specific receptors, but even in their absence, a
reception may occur in a small fraction of the eggs; the chances are now
about the same for both homologous and heterologous sperm. The receptors are, thus, specific factors that increase the rate of fertilization
of spermatozoa with fitting acrosomal surface.
The difference between the experiments of T. Hultin (1948a) and
those of Hagström (1959) is that the former worker used a commercial
trypsin preparation which also contains enzymes other than trypsin,
whereas the latter used crystalline trypsin. On the whole, the same
JOHN RUNNSTRÖM
of Arbacia lixula (Hultin, 1948b). Addition of egg water from Arbacia
eggs, however, enhanced the cross-fertilization with sperm from Arbacia
when the vitelline membrane was removed. Addition of rabbit serum,
bovine albumin, or glycine had the same effect as egg water (see also,
Runnström, 1952a, p. 72; Hagström, 1956b). It is obvious, therefore,
that unspecific factors—primarily increasing the motility of the spermatozoa—may manifest the protecting effect of the vitelline membrane.
The results from the crosses in which Arbacia sperm were used, thus, do
not invalidate Hultin's conclusion regarding the role of the vitelline membrane. It seems very likely that the vitelline membrane has a specific
structure that makes it a reception site for the spermatozoa. Moreover, it
protects the egg against cross-fertilization, but, as Hagström (1959)
pointed out, deeper layers of the egg surface may take part in this protection (see further Section II,F). Hagström's data show quantitatively
that the rate of fertilization is lower in cross-fertilization between different genera than in homologous fertilization, even if almost 100% fertilization will eventually be attained in the former, as, for example, in
the cross between Psammechinus
female and Paracentrotus
male. In the
case presented in Hagström's Fig. 2 (1959), the cross-fertilization had a
50% fertilization value of about 80 sec, whereas the corresponding value
was 20 sec in the homologous fertilization. The acrosomal region of the
spermatozoon of Paracentrotus
does not fit as well to the dominating
egg receptor as that of the homologous spermatozoon. Nevertheless, there
is a certain degree of fitness which gives a measurable rate of fertilization. In other crosses, for example, between Sphaerechinus
female and
Paracentrotus
male, the rate of fertilization was very low (50% fertilization not being attained in 2-3 hr) ; following a pretreatment with
0.001% trypsin for 10 min, the rate of cross-fertilization increased to
about the rate found in homologous fertilization after trypsin pretreatment of the eggs (Hagström, loc. cit., Figs. 3 and 4). After removal of
the species-specific receptors by trypsin pretreatment, both homologous
and heterologous sperm are almost in the same situation when attacking
the egg surface. The acrosome of homologous spermatozoon does not
meet the rate increasing specific receptors, but even in their absence, a
reception may occur in a small fraction of the eggs; the chances are now
about the same for both homologous and heterologous sperm. The receptors are, thus, specific factors that increase the rate of fertilization
of spermatozoa with fitting acrosomal surface.
The difference between the experiments of T. Hultin (1948a) and
those of Hagström (1959) is that the former worker used a commercial
trypsin preparation which also contains enzymes other than trypsin,
whereas the latter used crystalline trypsin. On the whole, the same