4. ANALYSIS OF FACTORS INVOLVED IN SYMBIOSIS
133
form spores are expelled by involuntary escape despite the fact that
they undergo one phase of their development (sexual reproduction in
the case of A. eberthi) in the cells lining the host’s gut.
In the case of another sporozoan, Nematopsis ostrearum, which is
found in the mantle, adductor muscle, heart, gills, labial palps, and
perhaps other organs of oysters as vegetative spores or sporozoites
(Prytherch, 1938, 1940; Sprague and Orr, 1955), the exact mechanism
of escape remains undetermined. Feng (1958) has demonstrated that
this parasite does escape by transplanting oysters, Crassostrea virginica,
with high and low initial infections into areas of low and high infections,
respectively. Subsequent checks have revealed that the transplanted
oysters attain the characteristic level of infections of oysters native to
that area. Thus a dynamic equilibrium of elimination (escape) and
reinfection appears to exist. Feng has postulated that the spores may be
phagocytized by the oyster’s leucocytes and are eliminated across epithelial surfaces like experimentally introduced India ink and vertebrate
erythrocytes (Stauber, 1950; Tripp, 1958a) but this has yet to be
demonstrated. If his postulation is correct, then the escape of Nematopsis ostrearum from oysters is effected not by its own motility or behavior,
but by the host’s cells. This represents another possible method of
escape, herein designated as cellular escape.
Our present knowledge concerning the escape of trematode cercariae,
which is the best understood among zoosymbionts, is based mainly on
schistosome cercariae. Leiper (1915)) working with Schistosoma
rnansoni, has observed that cercariae are discharged in puffs and quite
independently of the passage of feces. Lutz (1919)) who also studied
S. mansoni, has suggested that all channels on the mollusc’s body
surface are used and has even reported emergence to take place via
the intestinal canal. Faust and Meleney (1924) maintain that S.
japonicurn cercariae accumulate in the spaces between the hepatopancreatic tubules and cause the tunica propria which surrounds the
entire gland to burst, thus permitting the cercariae to escape in swarms
between the body wall and the shell of the snail. Faust and Hoffman
(1934) have reported the same for X. mansoni cercariae.
Brumpt (1941) has demonstrated S. mansoni cercariae within the
eggs of Australorbis glabratus, a phenomenon verified by Etges and
Gresso (1965), and has concluded that escape occurs via the snail’s
genital ducts. Duke (1952)) also working with 8. mansoni, has shown
that cercarial exodus takes place chiefly at the pseudobranch and collar
and has suggested that they travel with the main flow of the venous
blood, which passes down alongside the rectum, before being returned
to the heart via the mantle. Furthermore, he regards the escape as an
133
form spores are expelled by involuntary escape despite the fact that
they undergo one phase of their development (sexual reproduction in
the case of A. eberthi) in the cells lining the host’s gut.
In the case of another sporozoan, Nematopsis ostrearum, which is
found in the mantle, adductor muscle, heart, gills, labial palps, and
perhaps other organs of oysters as vegetative spores or sporozoites
(Prytherch, 1938, 1940; Sprague and Orr, 1955), the exact mechanism
of escape remains undetermined. Feng (1958) has demonstrated that
this parasite does escape by transplanting oysters, Crassostrea virginica,
with high and low initial infections into areas of low and high infections,
respectively. Subsequent checks have revealed that the transplanted
oysters attain the characteristic level of infections of oysters native to
that area. Thus a dynamic equilibrium of elimination (escape) and
reinfection appears to exist. Feng has postulated that the spores may be
phagocytized by the oyster’s leucocytes and are eliminated across epithelial surfaces like experimentally introduced India ink and vertebrate
erythrocytes (Stauber, 1950; Tripp, 1958a) but this has yet to be
demonstrated. If his postulation is correct, then the escape of Nematopsis ostrearum from oysters is effected not by its own motility or behavior,
but by the host’s cells. This represents another possible method of
escape, herein designated as cellular escape.
Our present knowledge concerning the escape of trematode cercariae,
which is the best understood among zoosymbionts, is based mainly on
schistosome cercariae. Leiper (1915)) working with Schistosoma
rnansoni, has observed that cercariae are discharged in puffs and quite
independently of the passage of feces. Lutz (1919)) who also studied
S. mansoni, has suggested that all channels on the mollusc’s body
surface are used and has even reported emergence to take place via
the intestinal canal. Faust and Meleney (1924) maintain that S.
japonicurn cercariae accumulate in the spaces between the hepatopancreatic tubules and cause the tunica propria which surrounds the
entire gland to burst, thus permitting the cercariae to escape in swarms
between the body wall and the shell of the snail. Faust and Hoffman
(1934) have reported the same for X. mansoni cercariae.
Brumpt (1941) has demonstrated S. mansoni cercariae within the
eggs of Australorbis glabratus, a phenomenon verified by Etges and
Gresso (1965), and has concluded that escape occurs via the snail’s
genital ducts. Duke (1952)) also working with 8. mansoni, has shown
that cercarial exodus takes place chiefly at the pseudobranch and collar
and has suggested that they travel with the main flow of the venous
blood, which passes down alongside the rectum, before being returned
to the heart via the mantle. Furthermore, he regards the escape as an