2
time his paper remained the principal source of information
on this topic. In Flustra foliacea , Grant discovered eggs
[oocytes] developing in the proximal part of the zooid and a
mature “ovum” [embryo] occupying its distal part, where it
was surrounded by a “helmet-shaped capsule” [ovicell] separating the maturing larva from the zooidal cavity. Grant
described the distribution of fertile zooids in the colony and
observed developing embryos and larval release, swimming
and settlement. He appears to have been the fi rst researcher
who described sperm and larval metamorphosis in bryozoans.
These observations showed the ovicell to be an incubation
site, not an ovary, although Grant neither emphasized his
discovery nor recognized its implications. Later Thompson
( 1830 ), Milne-Edwards ( 1836 ), Van Beneden ( 1844a ) and
Allman ( 1856 ) reported that in some ctenostome and cheilostome bryozoans “ova” developed on the zooidal wall, but it
was Huxley ( 1856 , p. 192) who fi nally stated that the ovicell
is merely a “marsupial pouch”.
Johnston briefl y summarized the scarce data on bryozoan
reproduction in his monograph ( 1847 ). He concluded that
“Polyzoa” were hermaphrodites whose eggs developed from
the epithelial lining of the zooid wall and that the mature egg
entered the zooidal cavity where it grew and was later fertilized by sperms formed in the same zooid. It should be noted
that Nordmann ( 1839 ) and Van Beneden ( 1844a ) had been the
fi rst to suggest self-fertilization in bryozoans (intracolonial
and intrazooidal, correspondingly), and this opinion persisted
in the literature for 150 years (see below).
Following general opinion, Johnston ( 1847 , p. 262) wrote
that in many bryozoan genera eggs were also formed in ovicells. Soon, however, Huxley ( 1856 ) demonstrated convincingly that ovicells were exclusively brooding structures. In
addition, he recorded the difference in the position of the
ovary in different cheilostome species: on the funiculus and
on the basal wall of the maternal zooid. Huxley’s observations and conclusions were independently supported by
Nitsche ( 1869 ), who reported that the ovary was formed
from the “endocyst” [epithelial lining of the body wall].
Another important contribution was that of Smitt ( 1865 ),
who described and superbly illustrated certain structural and
developmental features of gonads and gametes in several
cheilostome bryozoans. In particular, he demonstrated the
cellular composition of the ovary wall. One of his major
discoveries was oocyte doublets in the ovaries, which can be
clearly seen in his illustrations although he did not
understand the importance of this fi nding. Oocyte doublets
were soon described, but misinterpreted, by Claparède
( 1871 ) also. This researcher agreed with Huxley ( 1856 ),
Smitt ( 1865 ) and Nitsche ( 1869 ) concerning the incubatory
function of the ovicell, confi rmed earlier observations that
in different species the ovary might be located on the basal
wall of the cystid or on the funiculus and noted that the
female gonad changed its position relative to the developing
polypide. Moreover, Claparède was the fi rst to observe an
incipient ovary (in fact, early female cells) in the young
zooid bud.
In his seminal but almost forgotten paper, Joliet ( 1877 )
described details of sexual reproduction in ten species of
gymnolaemate bryozoans and concluded that both male and
female gonads developed at the expense of the funiculus.
Challenging widespread opinion, Joliet was the fi rst to suggest that bryozoans might have cross-fertilization since he
observed protandric hermaphrodite and gonochoristic zooids
and numerous sperm that could swim in seawater.
The next review appeared in the monograph of Hincks
( 1880 ), who summarized the data obtained by the above
authors as well as the results of his own observations on bryozoan reproduction. He concluded that the testis or testes in
bryozoans were always formed from the “endosarc” (funicular tissue). The ovary, according to him, usually had the same
origin but when it was located on the cystid wall its origin was
uncertain – it could be “endosarc” (strands of funicular tissue)
or “endocyst” (epidermal layer of the body wall). While
agreeing with Joliet ( 1877 ) about the possibility of cross-fertilization, Hinck considered self- fertilization to be the rule.
Likewise, while agreeing with Huxley ( 1856 ), Nitsche ( 1869 )
and Joliet concerning the incubatory function of ovicells, he
nevertheless thought that eggs might in some cases originate
in them (Ostrovsky 2008a ; Ostrovsky et al. 2008 ; see also
Appendix I for details).
Vigelius ( 1882 , 1884a , b , 1886 ), who was the fi rst to apply
anatomical sectioning to Bryozoa, should be credited with the
most complete and precise descriptions of sexual reproduction in cheilostomes in the early period of bryozoan studies.
He suggested that in different species the ovary originated
either from the “parietal layer” of the body wall or from
“mesenchymal parenchyma” (funicular tissue). When he
found in one and the same colony gonochoristic zooids with
simultaneous maturation of gametes, and hermaphrodite
zooids with different terms of the gamete maturation, Vigelius
agreed with Joliet ( 1877 ) concerning cross- fertilization. On
the other hand, the simultaneous presence of male and female
gametes in hermaphrodite zooids in another species led him
to infer intrazooidal self-fertilization (Vigelius 1886 ).
Kraepelin ( 1887 ) thought that both types of gonads were
formed from the peritoneum. Pergens ( 1889 ), the fi rst
researcher to observe the transfer of the oocyte into the
ovicell, noted the presence of a “chorion” [fertilization envelope] around the ovulated oocyte. Prouho ( 1889 , 1892 ), who
undertook a detailed study of sexual reproduction in eight
gymnolaemate species (mostly Ctenostomata), discovered
brooding and non-brooding species within the same genus,
Alcyonidium . Prouho sided with the opinion about selffertilization in bryozoans.
A prominent landmark in research on sexual reproduction
in marine bryozoans was the monograph of Calvet ( 1900 ),
1 Reproductive Patterns of Gymnolaemate Bryozoa: General Overview and Comparative Analysis
time his paper remained the principal source of information
on this topic. In Flustra foliacea , Grant discovered eggs
[oocytes] developing in the proximal part of the zooid and a
mature “ovum” [embryo] occupying its distal part, where it
was surrounded by a “helmet-shaped capsule” [ovicell] separating the maturing larva from the zooidal cavity. Grant
described the distribution of fertile zooids in the colony and
observed developing embryos and larval release, swimming
and settlement. He appears to have been the fi rst researcher
who described sperm and larval metamorphosis in bryozoans.
These observations showed the ovicell to be an incubation
site, not an ovary, although Grant neither emphasized his
discovery nor recognized its implications. Later Thompson
( 1830 ), Milne-Edwards ( 1836 ), Van Beneden ( 1844a ) and
Allman ( 1856 ) reported that in some ctenostome and cheilostome bryozoans “ova” developed on the zooidal wall, but it
was Huxley ( 1856 , p. 192) who fi nally stated that the ovicell
is merely a “marsupial pouch”.
Johnston briefl y summarized the scarce data on bryozoan
reproduction in his monograph ( 1847 ). He concluded that
“Polyzoa” were hermaphrodites whose eggs developed from
the epithelial lining of the zooid wall and that the mature egg
entered the zooidal cavity where it grew and was later fertilized by sperms formed in the same zooid. It should be noted
that Nordmann ( 1839 ) and Van Beneden ( 1844a ) had been the
fi rst to suggest self-fertilization in bryozoans (intracolonial
and intrazooidal, correspondingly), and this opinion persisted
in the literature for 150 years (see below).
Following general opinion, Johnston ( 1847 , p. 262) wrote
that in many bryozoan genera eggs were also formed in ovicells. Soon, however, Huxley ( 1856 ) demonstrated convincingly that ovicells were exclusively brooding structures. In
addition, he recorded the difference in the position of the
ovary in different cheilostome species: on the funiculus and
on the basal wall of the maternal zooid. Huxley’s observations and conclusions were independently supported by
Nitsche ( 1869 ), who reported that the ovary was formed
from the “endocyst” [epithelial lining of the body wall].
Another important contribution was that of Smitt ( 1865 ),
who described and superbly illustrated certain structural and
developmental features of gonads and gametes in several
cheilostome bryozoans. In particular, he demonstrated the
cellular composition of the ovary wall. One of his major
discoveries was oocyte doublets in the ovaries, which can be
clearly seen in his illustrations although he did not
understand the importance of this fi nding. Oocyte doublets
were soon described, but misinterpreted, by Claparède
( 1871 ) also. This researcher agreed with Huxley ( 1856 ),
Smitt ( 1865 ) and Nitsche ( 1869 ) concerning the incubatory
function of the ovicell, confi rmed earlier observations that
in different species the ovary might be located on the basal
wall of the cystid or on the funiculus and noted that the
female gonad changed its position relative to the developing
polypide. Moreover, Claparède was the fi rst to observe an
incipient ovary (in fact, early female cells) in the young
zooid bud.
In his seminal but almost forgotten paper, Joliet ( 1877 )
described details of sexual reproduction in ten species of
gymnolaemate bryozoans and concluded that both male and
female gonads developed at the expense of the funiculus.
Challenging widespread opinion, Joliet was the fi rst to suggest that bryozoans might have cross-fertilization since he
observed protandric hermaphrodite and gonochoristic zooids
and numerous sperm that could swim in seawater.
The next review appeared in the monograph of Hincks
( 1880 ), who summarized the data obtained by the above
authors as well as the results of his own observations on bryozoan reproduction. He concluded that the testis or testes in
bryozoans were always formed from the “endosarc” (funicular tissue). The ovary, according to him, usually had the same
origin but when it was located on the cystid wall its origin was
uncertain – it could be “endosarc” (strands of funicular tissue)
or “endocyst” (epidermal layer of the body wall). While
agreeing with Joliet ( 1877 ) about the possibility of cross-fertilization, Hinck considered self- fertilization to be the rule.
Likewise, while agreeing with Huxley ( 1856 ), Nitsche ( 1869 )
and Joliet concerning the incubatory function of ovicells, he
nevertheless thought that eggs might in some cases originate
in them (Ostrovsky 2008a ; Ostrovsky et al. 2008 ; see also
Appendix I for details).
Vigelius ( 1882 , 1884a , b , 1886 ), who was the fi rst to apply
anatomical sectioning to Bryozoa, should be credited with the
most complete and precise descriptions of sexual reproduction in cheilostomes in the early period of bryozoan studies.
He suggested that in different species the ovary originated
either from the “parietal layer” of the body wall or from
“mesenchymal parenchyma” (funicular tissue). When he
found in one and the same colony gonochoristic zooids with
simultaneous maturation of gametes, and hermaphrodite
zooids with different terms of the gamete maturation, Vigelius
agreed with Joliet ( 1877 ) concerning cross- fertilization. On
the other hand, the simultaneous presence of male and female
gametes in hermaphrodite zooids in another species led him
to infer intrazooidal self-fertilization (Vigelius 1886 ).
Kraepelin ( 1887 ) thought that both types of gonads were
formed from the peritoneum. Pergens ( 1889 ), the fi rst
researcher to observe the transfer of the oocyte into the
ovicell, noted the presence of a “chorion” [fertilization envelope] around the ovulated oocyte. Prouho ( 1889 , 1892 ), who
undertook a detailed study of sexual reproduction in eight
gymnolaemate species (mostly Ctenostomata), discovered
brooding and non-brooding species within the same genus,
Alcyonidium . Prouho sided with the opinion about selffertilization in bryozoans.
A prominent landmark in research on sexual reproduction
in marine bryozoans was the monograph of Calvet ( 1900 ),
1 Reproductive Patterns of Gymnolaemate Bryozoa: General Overview and Comparative Analysis