302
Some 4–6 eggs are released through the reduced intertentacular organ, being further brooded in the cavity of the vestibulum when the polypide is retracted and exposed outside
when it is extended. Eggs separated from the maternal zooid
did not develop successfully. In Victorella , both ovarian and
spermatogenic tissue are on the cystid wall in the distal part
of the hermaphrodite zooid. Eggs are numerous, but, as in
Bulbella , mature sequentially, exiting through the supraneural pore and sinking into the special protuberance of the body
wall that forms the invagination or brood sac. When the polypide is retracted, embryos (normally three) are placed in the
vestibulum. Thus, Silén’s suggestion concerning the method
of embryo-sac formation in ctenostomes was not supported
(discussed in Ström 1977 ). Braem ( 1951 ) also recorded
brooding in the vestibulum of Bowerbankia gracilis (as
B . caudata ) following polypide degeneration. The ovary is
located in the middle part of the hermaphrodite zooid on the
cystid wall at the site of attachment of the funiculus.
Spermatogenic tissue was found on the cystid wall also, but
more proximally. The mature egg moves via an intertentacular
pore between the degenerating mouth and anus into the
tentacle sheath. From there it is presumed to pass the diaphragm to be surrounded by the vestibular wall. These fi ndings accorded with those of Joliet ( 1877a ) on Walkeria uva
(as Valkeria cuscuta ). Additionally, both ovarian and spermatogenic tissue were found on the cystid wall in the distal
part of the hermaphrodite zooids of the non-brooding ctenostome Victorella pavida . As in other broadcasters, its oocytes
are small, maturing and ovulating in cohorts; after ovulation
they are irregular in shape. In addition, an intertentacular
organ was found and studied in histological sections. Much
confusion surrounds this broadcasting species, which is considered to be a brooder in the monographs of Hyman ( 1959 )
and Hayward ( 1985 ). This contradiction is discussed and
explained by Jebram and Everitt ( 1982 ).
Despite the fact that many researchers kept bryozoans
alive for long periods, there are very few published observations on their reproductive activities. In his subsequent paper,
Silén ( 1945 ) documented summer observations on the reproductive biology of several gymnolaemate species under
experimental conditions, comparing brooding and nonbrooding species. He noted simultaneously hermaphrodite
zooids in Membranipora membranacea . In Callopora
dumerilii (as C . dumerili ) (and with reference to Escharella
immersa and Fenestrulina malusii (as F . malusi )) he observed
and carefully described ovicell development, oocyte growth,
ovulation and a post-ovulatory period as well as larval behaviour. Silén stated that regression of the wall of the follicle
containing a mature egg is triggered by movements of the
polypide caecum (see also Gerwerzhagen 1913 ), which further result in shifting the ovulated egg to the distal part of the
maternal zooid. He described oviposition and synchronized
development of the embryo and the succeeding oocyte, repeating the idea of Marcus ( 1938a ) about hormonal regulation of
this synchrony. Development of the ooecium was said to be
triggered by the onset of ovarian activity through hormonal
regulation also. In aquaria, it took approximately two weeks
for each egg to mature in the ovary of C. dumerilii .
Development of the embryo in the ovicell has the same duration, and these events are correlated in time. Thus, the
repeated use of the ovicell (at least three times) was proven
(see Joliet 1877a ). It was also suggested that the limited
space of the incubation cavity restricted the number of
oocytes produced in the ovary. The “ Membrana vitellina ”
[fertilization envelope] was found to surround an embryo in
the ovicell. Since embryos could not develop outside the ovicell when experimentally released through breakage, it was
concluded that the chemical composition of the fl uid inside
the incubation cavity differs from that of sea-water, and the
ooecial vesicle must be responsible for that. The intertentacular organ and coelomopore were considered homologous
and secondarily evolved structures, used not only for egg
release, but possibly also for the acceptance of alien sperm.
Thus, Silén tended to favour the concept of cross- fertilization.
Larval release through the body wall following development
in an “embryonary” [brood sac] was suggested as the primitive condition. Such a condition seems to have been found in
the ctenostome Nolella, but that taxon also has a supraneural
pore (recorded by Marcus 1938a ) that Silén thought initially
evolved in connection with some other function, for instance
sperm entry.
Crucially, it was realized that further progress in research
on bryozoan reproduction would be impossible without seasonal observations and studies of life history. Kuznetzov
( 1941 ) was one of the fi rst to make a comparative study of
the life cycles about 60 bryozoan species, and proposed the
fi rst classifi cation based on the number of generations, periods of their reproduction and duration of life span. Four patterns were identifi ed based on the above combination of
characters. Borg ( 1947 ) undertook an investigation of the life
cycle of the cheilostome Einhornia crustulenta (as Electra ),
using material collected throughout the year. Judging from
his description, zooids are simultaneously hermaphrodite in
this species. He correctly noted that the term “testis” could
hardly be applied to the diffuse male elements that started
their development from the mesodermal lining of the cystid
wall as well as on funicular strands. He described ovaries as
being one or several, developing in connection with the caecum, and often referred to the paper of Schulz ( 1901 ), who
also mentioned the plural nature of the ovary in this species.
The maximal number of eggs in one ovary was up to sixteen.
Borg recorded the presence/absence of gonads and state of
the polypide throughout the seasons, suggesting a correlation
between polypide cycling and sexual reproduction. Moreover,
he stated that the main function of cycling is not excretion,
and that “the de- and regeneration of the polypides must have
Appendices
Some 4–6 eggs are released through the reduced intertentacular organ, being further brooded in the cavity of the vestibulum when the polypide is retracted and exposed outside
when it is extended. Eggs separated from the maternal zooid
did not develop successfully. In Victorella , both ovarian and
spermatogenic tissue are on the cystid wall in the distal part
of the hermaphrodite zooid. Eggs are numerous, but, as in
Bulbella , mature sequentially, exiting through the supraneural pore and sinking into the special protuberance of the body
wall that forms the invagination or brood sac. When the polypide is retracted, embryos (normally three) are placed in the
vestibulum. Thus, Silén’s suggestion concerning the method
of embryo-sac formation in ctenostomes was not supported
(discussed in Ström 1977 ). Braem ( 1951 ) also recorded
brooding in the vestibulum of Bowerbankia gracilis (as
B . caudata ) following polypide degeneration. The ovary is
located in the middle part of the hermaphrodite zooid on the
cystid wall at the site of attachment of the funiculus.
Spermatogenic tissue was found on the cystid wall also, but
more proximally. The mature egg moves via an intertentacular
pore between the degenerating mouth and anus into the
tentacle sheath. From there it is presumed to pass the diaphragm to be surrounded by the vestibular wall. These fi ndings accorded with those of Joliet ( 1877a ) on Walkeria uva
(as Valkeria cuscuta ). Additionally, both ovarian and spermatogenic tissue were found on the cystid wall in the distal
part of the hermaphrodite zooids of the non-brooding ctenostome Victorella pavida . As in other broadcasters, its oocytes
are small, maturing and ovulating in cohorts; after ovulation
they are irregular in shape. In addition, an intertentacular
organ was found and studied in histological sections. Much
confusion surrounds this broadcasting species, which is considered to be a brooder in the monographs of Hyman ( 1959 )
and Hayward ( 1985 ). This contradiction is discussed and
explained by Jebram and Everitt ( 1982 ).
Despite the fact that many researchers kept bryozoans
alive for long periods, there are very few published observations on their reproductive activities. In his subsequent paper,
Silén ( 1945 ) documented summer observations on the reproductive biology of several gymnolaemate species under
experimental conditions, comparing brooding and nonbrooding species. He noted simultaneously hermaphrodite
zooids in Membranipora membranacea . In Callopora
dumerilii (as C . dumerili ) (and with reference to Escharella
immersa and Fenestrulina malusii (as F . malusi )) he observed
and carefully described ovicell development, oocyte growth,
ovulation and a post-ovulatory period as well as larval behaviour. Silén stated that regression of the wall of the follicle
containing a mature egg is triggered by movements of the
polypide caecum (see also Gerwerzhagen 1913 ), which further result in shifting the ovulated egg to the distal part of the
maternal zooid. He described oviposition and synchronized
development of the embryo and the succeeding oocyte, repeating the idea of Marcus ( 1938a ) about hormonal regulation of
this synchrony. Development of the ooecium was said to be
triggered by the onset of ovarian activity through hormonal
regulation also. In aquaria, it took approximately two weeks
for each egg to mature in the ovary of C. dumerilii .
Development of the embryo in the ovicell has the same duration, and these events are correlated in time. Thus, the
repeated use of the ovicell (at least three times) was proven
(see Joliet 1877a ). It was also suggested that the limited
space of the incubation cavity restricted the number of
oocytes produced in the ovary. The “ Membrana vitellina ”
[fertilization envelope] was found to surround an embryo in
the ovicell. Since embryos could not develop outside the ovicell when experimentally released through breakage, it was
concluded that the chemical composition of the fl uid inside
the incubation cavity differs from that of sea-water, and the
ooecial vesicle must be responsible for that. The intertentacular organ and coelomopore were considered homologous
and secondarily evolved structures, used not only for egg
release, but possibly also for the acceptance of alien sperm.
Thus, Silén tended to favour the concept of cross- fertilization.
Larval release through the body wall following development
in an “embryonary” [brood sac] was suggested as the primitive condition. Such a condition seems to have been found in
the ctenostome Nolella, but that taxon also has a supraneural
pore (recorded by Marcus 1938a ) that Silén thought initially
evolved in connection with some other function, for instance
sperm entry.
Crucially, it was realized that further progress in research
on bryozoan reproduction would be impossible without seasonal observations and studies of life history. Kuznetzov
( 1941 ) was one of the fi rst to make a comparative study of
the life cycles about 60 bryozoan species, and proposed the
fi rst classifi cation based on the number of generations, periods of their reproduction and duration of life span. Four patterns were identifi ed based on the above combination of
characters. Borg ( 1947 ) undertook an investigation of the life
cycle of the cheilostome Einhornia crustulenta (as Electra ),
using material collected throughout the year. Judging from
his description, zooids are simultaneously hermaphrodite in
this species. He correctly noted that the term “testis” could
hardly be applied to the diffuse male elements that started
their development from the mesodermal lining of the cystid
wall as well as on funicular strands. He described ovaries as
being one or several, developing in connection with the caecum, and often referred to the paper of Schulz ( 1901 ), who
also mentioned the plural nature of the ovary in this species.
The maximal number of eggs in one ovary was up to sixteen.
Borg recorded the presence/absence of gonads and state of
the polypide throughout the seasons, suggesting a correlation
between polypide cycling and sexual reproduction. Moreover,
he stated that the main function of cycling is not excretion,
and that “the de- and regeneration of the polypides must have
Appendices