287
lata ). He also observed motile intracoelomic spermatozoids
and egg/embryo growth inside the “enveloping membrane”
[introvert] accompanied by polypide degeneration, followed
by larval release, in Bowerbankia sp.
Allman ( 1856 ) carefully described the shape, position
and content of male and female gonads in Paludicella articulata (as P . ehrenbergi ) with numerous eggs and sperm at
various developmental stages. He stressed that they simultaneously developed inside the same zooids in this bryozoan.
In contrast with Farrella studied by Van Beneden ( 1844a ),
the testis was reported proximally on the body wall, at the
site of the funicular attachment in Paludicella . An ovary
containing more than 40 oocytes was found on the body
wall, also associated with another funicular strand, but this
time in the distal part of the zooid. Allman also described
gametic structure, divisions of spermatogonia, movement of
spermatozoids, their concentration in the body cavity and
grouping around the ovary. Interestingly, since Allman
believed that the polypide and cystid are distinct individuals
(zooids), budding one from another, he suggested that the
ovary and testis could be simplifi ed zooids too. Some scientists followed Allman, for instance, Salensky ( 1874 ) (for
further discussion see Nitsche 1871a , b ; Joliet 1877a ).
Finally, Allman presented a brilliant review of the studies on
freshwater Bryozoa, pointing out many of the most intriguing discoveries made at this time [for references to the early
work on Phylactolaemata see also Bronn ( 1862 ), Hyatt
( 1866–1868 ), Hincks ( 1880 ), Vigelius ( 1884b ), Marcus
( 1934 ) and Cori ( 1941 )].
The true function of the ovicell as a “marsupial pouch”
was fi rst recognized by Huxley ( 1856 , pp. 191–192),
although similar observations were published earlier by
Grant ( 1827 ) (see above). In young zooids of Bugula avicularia (as B . avicularis ), Huxley found a growing “ovum”
“attached to the funiculus … close to the stomach” (and
described the changes in its coloration from pale to reddish
during its maturation), and the testis on the basal zooid wall
at the site of attachment of the funiculus. Huxley wrote that
the form and structure of the testis are similar and its location the same in three other cheilostomes he studied. Huxley
stressed that an ovary with a ripening egg is situated at the
top of the funiculus in B. avicularia . In contrast, he noted
that the “ovarium”, which “rarely presents more than one or
two ova”, is not directly connected with the funiculus, being
placed in the middle of the basal wall in B . fl abellata , at the
“apex of the back” [i.e. in the corner between basal and distal
transverse walls] in B . plumosa , and on the distal part of the
basal wall in Scrupocellaria scruposa . Huxley noted ova
“commonly possessing a double germinal spot” in B. avicularia – probably the nucleoli of the oocyte doublets unrecognized by him. Huxley’s fi nal conclusion was that, following
“impregnation” [self-fertilization] “the ovum passes … into
the ovicell”.
Redfern ( 1858 , p. 100) observed “ova or statoblasts” and
“bodies [with] cilia”, [presumably embryos], when studying
Flustrellidra hispida (as Flustrella ). This author was one of
the fi rst who both described and illustrated in detail postlarval
development in marine bryozoans, but unfortunately his
paper has been forgotten.
Bronn ( 1862 ) made a general review of previous observations on bryozoan reproduction in his textbook, in which he
repeated the opinion, common at that time, regarding bryozoan self-fertilization, based on the simultaneous presence of
both sperm and eggs in the same zooid. One can fi nd a similar brief overview in the book by Busk ( 1859 ).
Smitt ( 1865 , p. 34) described and beautifully illustrated
aspects of gamete development and gonad structure in four
species of cheilostome and one cyclostome. Notably,
although describing the wall of the early “egg sac” [ovary] as
a “common and clear membrane”, in three instances Smitt
depicted it as partially consisting of cells. In mature ovaries
the ripening egg is described as being surrounded by an
epithelium- like cellular cover. In contrast, the majority of
researchers at that time illustrated it as a simple line, indicating a [non-cellular] membrane. Later Claparède ( 1871 , p.
166), Repiachoff ( 1876 , p. 140), Ostroumoff ( 1886a , p. 24,
1886b , p. 72) and Calvet ( 1900 , p. 293) described the ovary
wall as “zelligen Membran/Hülle [envelope]” or a “membrane cellulaire”, consisting of cells. Salensky ( 1874 ) wrote
that the ovary consists of two layers, one internal and composed of rounded cells [oocytes] and the other external and
composed of fl at and spindle-shaped cells [ovarian wall].
Smitt ( 1865 ) carefully described and measured the stages
of oocyte growth in ovaries of Escharella immersa (as Lepralia
peachii ) and S. scruposa , showing the gonad positioned in the
corner between basal and lateral walls in the middle or distal
part of the zooid in the former species, and between basal,
lateral and distal transverse walls in the latter. Scrupocellaria
scruposa was recognized as having both ovary and spermatogenic tissue (in the proximal part of the cystid on its transverse, lateral and basal walls) simultaneously within the same
zooid. One of Smitt’s interesting fi ndings (which he depicted
but did not understand) was oocyte development occurring in
pairs (doublets). In the ovaries of S . scruposa he depicted up to
four oocyte doublets (plus additional small cells that were possibly oogonia), clearly showing in drawings the differences
between the leading and succeeding doublets as well as
between the oocyte and its nurse cell in older doublets. The
leading oocyte has numerous yolk granules in the cytoplasm
and eventually becomes blood-red in colour. Fertilization was
said to be intrazooidal, with cleavage occurring in the ovicell.
In Membranipora membranacea (as Flustra ) the ovary
and testis were also both recorded in the same zooid: the
ovary was found lying on the basal wall in the middle, and
the testis on the transverse, lateral and basal walls in the
proximal part of the zooid. There were about 40 small
Appendices
lata ). He also observed motile intracoelomic spermatozoids
and egg/embryo growth inside the “enveloping membrane”
[introvert] accompanied by polypide degeneration, followed
by larval release, in Bowerbankia sp.
Allman ( 1856 ) carefully described the shape, position
and content of male and female gonads in Paludicella articulata (as P . ehrenbergi ) with numerous eggs and sperm at
various developmental stages. He stressed that they simultaneously developed inside the same zooids in this bryozoan.
In contrast with Farrella studied by Van Beneden ( 1844a ),
the testis was reported proximally on the body wall, at the
site of the funicular attachment in Paludicella . An ovary
containing more than 40 oocytes was found on the body
wall, also associated with another funicular strand, but this
time in the distal part of the zooid. Allman also described
gametic structure, divisions of spermatogonia, movement of
spermatozoids, their concentration in the body cavity and
grouping around the ovary. Interestingly, since Allman
believed that the polypide and cystid are distinct individuals
(zooids), budding one from another, he suggested that the
ovary and testis could be simplifi ed zooids too. Some scientists followed Allman, for instance, Salensky ( 1874 ) (for
further discussion see Nitsche 1871a , b ; Joliet 1877a ).
Finally, Allman presented a brilliant review of the studies on
freshwater Bryozoa, pointing out many of the most intriguing discoveries made at this time [for references to the early
work on Phylactolaemata see also Bronn ( 1862 ), Hyatt
( 1866–1868 ), Hincks ( 1880 ), Vigelius ( 1884b ), Marcus
( 1934 ) and Cori ( 1941 )].
The true function of the ovicell as a “marsupial pouch”
was fi rst recognized by Huxley ( 1856 , pp. 191–192),
although similar observations were published earlier by
Grant ( 1827 ) (see above). In young zooids of Bugula avicularia (as B . avicularis ), Huxley found a growing “ovum”
“attached to the funiculus … close to the stomach” (and
described the changes in its coloration from pale to reddish
during its maturation), and the testis on the basal zooid wall
at the site of attachment of the funiculus. Huxley wrote that
the form and structure of the testis are similar and its location the same in three other cheilostomes he studied. Huxley
stressed that an ovary with a ripening egg is situated at the
top of the funiculus in B. avicularia . In contrast, he noted
that the “ovarium”, which “rarely presents more than one or
two ova”, is not directly connected with the funiculus, being
placed in the middle of the basal wall in B . fl abellata , at the
“apex of the back” [i.e. in the corner between basal and distal
transverse walls] in B . plumosa , and on the distal part of the
basal wall in Scrupocellaria scruposa . Huxley noted ova
“commonly possessing a double germinal spot” in B. avicularia – probably the nucleoli of the oocyte doublets unrecognized by him. Huxley’s fi nal conclusion was that, following
“impregnation” [self-fertilization] “the ovum passes … into
the ovicell”.
Redfern ( 1858 , p. 100) observed “ova or statoblasts” and
“bodies [with] cilia”, [presumably embryos], when studying
Flustrellidra hispida (as Flustrella ). This author was one of
the fi rst who both described and illustrated in detail postlarval
development in marine bryozoans, but unfortunately his
paper has been forgotten.
Bronn ( 1862 ) made a general review of previous observations on bryozoan reproduction in his textbook, in which he
repeated the opinion, common at that time, regarding bryozoan self-fertilization, based on the simultaneous presence of
both sperm and eggs in the same zooid. One can fi nd a similar brief overview in the book by Busk ( 1859 ).
Smitt ( 1865 , p. 34) described and beautifully illustrated
aspects of gamete development and gonad structure in four
species of cheilostome and one cyclostome. Notably,
although describing the wall of the early “egg sac” [ovary] as
a “common and clear membrane”, in three instances Smitt
depicted it as partially consisting of cells. In mature ovaries
the ripening egg is described as being surrounded by an
epithelium- like cellular cover. In contrast, the majority of
researchers at that time illustrated it as a simple line, indicating a [non-cellular] membrane. Later Claparède ( 1871 , p.
166), Repiachoff ( 1876 , p. 140), Ostroumoff ( 1886a , p. 24,
1886b , p. 72) and Calvet ( 1900 , p. 293) described the ovary
wall as “zelligen Membran/Hülle [envelope]” or a “membrane cellulaire”, consisting of cells. Salensky ( 1874 ) wrote
that the ovary consists of two layers, one internal and composed of rounded cells [oocytes] and the other external and
composed of fl at and spindle-shaped cells [ovarian wall].
Smitt ( 1865 ) carefully described and measured the stages
of oocyte growth in ovaries of Escharella immersa (as Lepralia
peachii ) and S. scruposa , showing the gonad positioned in the
corner between basal and lateral walls in the middle or distal
part of the zooid in the former species, and between basal,
lateral and distal transverse walls in the latter. Scrupocellaria
scruposa was recognized as having both ovary and spermatogenic tissue (in the proximal part of the cystid on its transverse, lateral and basal walls) simultaneously within the same
zooid. One of Smitt’s interesting fi ndings (which he depicted
but did not understand) was oocyte development occurring in
pairs (doublets). In the ovaries of S . scruposa he depicted up to
four oocyte doublets (plus additional small cells that were possibly oogonia), clearly showing in drawings the differences
between the leading and succeeding doublets as well as
between the oocyte and its nurse cell in older doublets. The
leading oocyte has numerous yolk granules in the cytoplasm
and eventually becomes blood-red in colour. Fertilization was
said to be intrazooidal, with cleavage occurring in the ovicell.
In Membranipora membranacea (as Flustra ) the ovary
and testis were also both recorded in the same zooid: the
ovary was found lying on the basal wall in the middle, and
the testis on the transverse, lateral and basal walls in the
proximal part of the zooid. There were about 40 small
Appendices