288
oocytes of approximately the same size in the ovary and fi ve
ovulated oocytes in the distal part of the zooid. In Escharella
immersa Smitt found eggs in the zooid cavity and a developing
embryo in the ovicell. This fi nding was later used by
Claparède ( 1871 ) as evidence supporting Huxley’s hypothesis on the exclusively brooding function of the ovicells.
Additionally, Smitt recorded oogenesis and embryo development in autozooids (in an internal brood sac that was
described as a “membrane”) in Cryptosula pallasiana (as
Lepralia ) and described and depicted its larvae, also mentioning their settlement and metamorphosis (see also Smitt
1863 ). Since he did not fi nd sperm in some species, Smitt
suggested that, in contrast with normal eggs, fertilized in the
zooid cavity, some bryozoans possess a special kind of egg
that develops into embryos without fertilization. According
to him, this could happen either inside the ovicell [gonozooid] in Crisia or inside the autozooid in C . pallasiana . In a
subsequent paper, Smitt ( 1866 ) recorded an intertentacular
organ in Electra pilosa (as Membranipora ).
Nitsche’s ( 1869 ) observations were in accord with the
conclusions of Huxley ( 1856 ). Studying Bugula fl abellata ,
B . plumosa and Bicellariella ciliata (as Bicellaria ), Nitsche
proved that ovicells are not ovaries, but rather chambers for
incubation. He also considered Smitt’s ( 1865 ) data on
Scrupocellaria scruposa as further evidence. In addition,
Nitsche was the fi rst to describe ovicell development and
structure precisely in cheilostomes, taking B . ciliata as an
example. Among other details he recorded an embryophore,
describing it as an “epithelium of polygonal cells” ( 1869 , p.
4). As with Huxley, he showed that all three species studied
possessed simultaneously hermaphrodite zooids. In all of
them spermatogenic tissue develops in the proximal part of
zooids. Later, mature spermatozoids were seen in the rest of
the perigastric cavity. Nitsche thought that there was no special ovary in B . ciliata (and also other bugulids studied) and
that two or three oocytes (in all probability, there is an oocyte
doublet pictured in his Tab. 1, fi g. 15) were “budded” on the
internal surface of the “Endocyste” [epithelial lining of the
cystid wall]. Eggs are situated on the wall adjacent to the
neighbouring zooid approximately in the middle part of the
cystid, being surrounded by a thin membrane [ovary wall]. In
contrast, Joliet ( 1877a ) mainly found ovary development
within a funiculus in this and some other species. He wrote
that he was able to fi nd the ovary on the cystid wall in a few
instances only.
Nitsche ( 1869 ) described oocyte growth, accumulation of
yolk [as the granular structure of the cytoplasm] and ovulation, accompanied by the breakdown of the nucleus and the
subsequent disappearance of the “Membran” [rupture of the
ovary wall] in Bicellariella ciliata . He proposed that the possible method for oviposition was through the pore situated
between the basal part of the ooecium and the ooecial vesicle
in the base of the ovicell. He also described and illustrated
larval morphology in all three species, and larval behaviour,
settlement, metamorphosis and formation of the ancestrula
in B. fl abellata .
Based on his studies of Scrupocellaria scruposa and
Bugula avicularia , Claparède ( 1871 ) supported the opinions
of Huxley ( 1856 ) and Smitt ( 1865 ) and noted that the fertilized egg should be transferred to the ovicell. Describing
oogenesis in the fi rst species, he recorded the difference in
the development of a pair of oocytes (“gepaarte Eizellen”) in
the ovary lying on the basal wall in its distal part and surrounded by a common envelope [ovary wall] – one egg [the
leading oocyte] rapidly increases in size, becomes bright red
and shows granular cytoplasm, whereas another [the nurse
cell] remains small and colourless. Further, the mature egg
leaves the ovary, whereas the small one, as Claparède
thought, is ready to divide. Actually, the nurse cell either
leaves the ovary together with its sibling or stays. In both
cases it degenerates, whereas a new oocyte doublet is developed following division of the oogonium. Like Nitsche
( 1869 ), Claparède wrote that eggs develop via proliferation
of the “Endocyste” in both species. By this term he presumably meant both the epithelium of the cystid wall and the
polypide.
In contrast to Scrupocellaria , the ovary of B . avicularia
is situated in the upper part of the funiculus and the laterdeveloping testis in its lower part. Claparède was the fi rst to
observe and illustrate an incipient ovary, consisting of two
small round cells at a time when both the cystid and the
polypide are incompletely formed and there is no trace of
the funiculus. Stressing the origin of the ovary from the
“Endocyste”, Claparède wrote that young doublet is adjacent to the pharynx of the polypide bud, being surrounded
by the cell membrane [prospective ovary wall], the cells of
which do not differ from the cells of the “Endocyste” [i.e.
the peritoneal lining of the polypide]. As the polypide
grows, the position of the ovary changes relative to it.
Additionally, Claparède described and depicted larval settlement and metamorphosis and formation of ancestrula in
B . avicularia .
Salensky ( 1874 ), reporting on ovary development in
Bugula plumosa , stated that it corresponds to that of the polypide bud and is formed as a cell accumulation on the internal surface of the cystid, thus making these structures
homologous.
Studies of Repiachoff ( 1875 ) and Reinhard ( 1875 ) on
reproduction of Tendra zostericola showed that simultaneously hermaphrodite zooids occur in this species, contradicting Nordmann ( 1839 ), who described separate male and
female zooids (see above). Apart from those zooids possessing both gonads simultaneously, Repiachoff did, however,
also mention separate male and female zooids in colonies of
this species, but was in doubt whether there was true gonochorism or non-simultaneous development of the gonad in
Appendices
oocytes of approximately the same size in the ovary and fi ve
ovulated oocytes in the distal part of the zooid. In Escharella
immersa Smitt found eggs in the zooid cavity and a developing
embryo in the ovicell. This fi nding was later used by
Claparède ( 1871 ) as evidence supporting Huxley’s hypothesis on the exclusively brooding function of the ovicells.
Additionally, Smitt recorded oogenesis and embryo development in autozooids (in an internal brood sac that was
described as a “membrane”) in Cryptosula pallasiana (as
Lepralia ) and described and depicted its larvae, also mentioning their settlement and metamorphosis (see also Smitt
1863 ). Since he did not fi nd sperm in some species, Smitt
suggested that, in contrast with normal eggs, fertilized in the
zooid cavity, some bryozoans possess a special kind of egg
that develops into embryos without fertilization. According
to him, this could happen either inside the ovicell [gonozooid] in Crisia or inside the autozooid in C . pallasiana . In a
subsequent paper, Smitt ( 1866 ) recorded an intertentacular
organ in Electra pilosa (as Membranipora ).
Nitsche’s ( 1869 ) observations were in accord with the
conclusions of Huxley ( 1856 ). Studying Bugula fl abellata ,
B . plumosa and Bicellariella ciliata (as Bicellaria ), Nitsche
proved that ovicells are not ovaries, but rather chambers for
incubation. He also considered Smitt’s ( 1865 ) data on
Scrupocellaria scruposa as further evidence. In addition,
Nitsche was the fi rst to describe ovicell development and
structure precisely in cheilostomes, taking B . ciliata as an
example. Among other details he recorded an embryophore,
describing it as an “epithelium of polygonal cells” ( 1869 , p.
4). As with Huxley, he showed that all three species studied
possessed simultaneously hermaphrodite zooids. In all of
them spermatogenic tissue develops in the proximal part of
zooids. Later, mature spermatozoids were seen in the rest of
the perigastric cavity. Nitsche thought that there was no special ovary in B . ciliata (and also other bugulids studied) and
that two or three oocytes (in all probability, there is an oocyte
doublet pictured in his Tab. 1, fi g. 15) were “budded” on the
internal surface of the “Endocyste” [epithelial lining of the
cystid wall]. Eggs are situated on the wall adjacent to the
neighbouring zooid approximately in the middle part of the
cystid, being surrounded by a thin membrane [ovary wall]. In
contrast, Joliet ( 1877a ) mainly found ovary development
within a funiculus in this and some other species. He wrote
that he was able to fi nd the ovary on the cystid wall in a few
instances only.
Nitsche ( 1869 ) described oocyte growth, accumulation of
yolk [as the granular structure of the cytoplasm] and ovulation, accompanied by the breakdown of the nucleus and the
subsequent disappearance of the “Membran” [rupture of the
ovary wall] in Bicellariella ciliata . He proposed that the possible method for oviposition was through the pore situated
between the basal part of the ooecium and the ooecial vesicle
in the base of the ovicell. He also described and illustrated
larval morphology in all three species, and larval behaviour,
settlement, metamorphosis and formation of the ancestrula
in B. fl abellata .
Based on his studies of Scrupocellaria scruposa and
Bugula avicularia , Claparède ( 1871 ) supported the opinions
of Huxley ( 1856 ) and Smitt ( 1865 ) and noted that the fertilized egg should be transferred to the ovicell. Describing
oogenesis in the fi rst species, he recorded the difference in
the development of a pair of oocytes (“gepaarte Eizellen”) in
the ovary lying on the basal wall in its distal part and surrounded by a common envelope [ovary wall] – one egg [the
leading oocyte] rapidly increases in size, becomes bright red
and shows granular cytoplasm, whereas another [the nurse
cell] remains small and colourless. Further, the mature egg
leaves the ovary, whereas the small one, as Claparède
thought, is ready to divide. Actually, the nurse cell either
leaves the ovary together with its sibling or stays. In both
cases it degenerates, whereas a new oocyte doublet is developed following division of the oogonium. Like Nitsche
( 1869 ), Claparède wrote that eggs develop via proliferation
of the “Endocyste” in both species. By this term he presumably meant both the epithelium of the cystid wall and the
polypide.
In contrast to Scrupocellaria , the ovary of B . avicularia
is situated in the upper part of the funiculus and the laterdeveloping testis in its lower part. Claparède was the fi rst to
observe and illustrate an incipient ovary, consisting of two
small round cells at a time when both the cystid and the
polypide are incompletely formed and there is no trace of
the funiculus. Stressing the origin of the ovary from the
“Endocyste”, Claparède wrote that young doublet is adjacent to the pharynx of the polypide bud, being surrounded
by the cell membrane [prospective ovary wall], the cells of
which do not differ from the cells of the “Endocyste” [i.e.
the peritoneal lining of the polypide]. As the polypide
grows, the position of the ovary changes relative to it.
Additionally, Claparède described and depicted larval settlement and metamorphosis and formation of ancestrula in
B . avicularia .
Salensky ( 1874 ), reporting on ovary development in
Bugula plumosa , stated that it corresponds to that of the polypide bud and is formed as a cell accumulation on the internal surface of the cystid, thus making these structures
homologous.
Studies of Repiachoff ( 1875 ) and Reinhard ( 1875 ) on
reproduction of Tendra zostericola showed that simultaneously hermaphrodite zooids occur in this species, contradicting Nordmann ( 1839 ), who described separate male and
female zooids (see above). Apart from those zooids possessing both gonads simultaneously, Repiachoff did, however,
also mention separate male and female zooids in colonies of
this species, but was in doubt whether there was true gonochorism or non-simultaneous development of the gonad in
Appendices