293
stomes, noting that it is accompanied by strong compression
of the egg and occurs when the polypide degenerates; up
until now, Gerwerzhagen ( 1913 ) had been thought to be the
fi rst to describe this phenomenon. Nielsen ( 1981 ) has
described oviposition in Fenestrulina miramara (described
as F . malusii ) as being undertaken by the everted lophophore
and almost without the egg deformation (see also below);
however, Pergen’s ( 1889 ) description is very realistic, and it
is unclear why oviposition is so different in congeneric species. A further important observation was that the ovary continued producing ova during polypide recycling, in accord
with the observations of Van Beneden ( 1844b ) and Vigelius
( 1884a ). Although fi nding only gonochoristic zooids,
Pergens believed that the sex of the zooid could change since
he recorded “spermatosporen” in ovicelled zooids. He also
observed a zygote and two polar bodies in the ovicell.
The classical works of Prouho ( 1889 , 1892 ) revealed different methods of brooding in several ctenostome bryozoans,
as well as demonstrating the presence of both brooding and
non-brooding species within the same ctenostome genus,
Alcyonidium . Non-brooder A. albidum has simultaneously
hermaphrodite zooids, with an ovary developing on the
funiculus and spermatogenic tissue on the cystid wall in the
proximal region. Judging from Prouho illustrations, the
ovary contains up to 18 small oocytes and up to three ovulated eggs occur in the body cavity. Prouho ( 1889 , p. 197)
described the “transparent and … delicate shell” [vitelline
membrane] surrounding the ovulated eggs and observed
their release through the intertentacular organ, proving that it
is an oviduct. He also suggested that fertilization possibly
occurred prior to the appearance of the “shell.”
Using anatomical sections, Prouho investigated the structure of the intertentacular organ in Electra pilosa (as Membranipora ) and Alcyonidium duplex . He observed egg release
through the “genital pore” [supraneural coelomopore] in the
non-brooding ctenostome Hypophorella expansa , thus showing that Ehlers ( 1876 ) was mistaken when he wrote that he
observed an intertentacular organ in the retracted polypides in
this species. Brooding within the introvert was described in
four species: Pherusella tubulosa (as Pherusa ), Flustrellidra
hispida (as Flustrella ), Alcyonidium variegatum and A .
duplex . In three of them the polypide degenerates, and several embryos are brooded simultaneously: 4–5 in the fi rst
two species [there can be up to eight embryos in F . hispida
according to Hayward ( 1985 )], and 6–8 in the third (it is not
clear from Prouho’s description how many embryos are
simultaneously brooded in A . variegatum ). According to his
description, in A . duplex the male germ cells are developed
on the funiculus of the fi rst polypide, at the site of its attachment to the stomach; they then migrate to the body wall,
establishing the gonad. An ovary is formed in the place
where the funiculus of the second polypide (whose bud coexists for some time with the fi rst one) attaches to the body
wall. There are 7–9 (up to 11) oocytes seen in the ovary in
Prouho’s illustrations. The ovulated eggs are irregular in
shape. In contrast with the fi rst polypide, which fi nally
degenerates, the polypide forming the ovary has an intertentacular organ. Released eggs stick to the polypide diaphragm
region [presumably, by their fertilization envelopes], being
withdrawn into the vestibulum during polypide retractions
and exposed when it expands. Later the third polypide forms
a new ovary and has the same structure as the second one that
degenerates. No new testis develops in the zooid.
In three species with a cyphonautes larva ( Electra pilosa ,
A . albidum and H . expansa ) ovulated eggs are of irregular
shape and are said to possess “slow ameboidal movements”
in the zooid cavity (Prouho 1892 , p. 608). They are surrounded by the “vitelline membrane” that was closely
apposed to the oocyte, and the elevation of the fertilization
envelope was described to occur after the passage of the eggs
through the intertentacular organ or supraneural coelomopore. Prouho recorded the subsequent appearance of two
polar bodies in the perivitelline space of recently spawned
zygotes in these species.
In Nolella dilatata (as Cylindroecium dilatatum ) Prouho
found, as he thought, internal brooding. According to his
description and fi gure explanations ( 1892 , pl. 14, fi gs 14–17),
2–3 “eggs” are incubated, adhering to the internal surface of
the zooid wall. Larvae were presumed to leave the zooid coelom through a rupture of this wall. It is also depicted that the
embryos are enlarged during brooding, with the youngest
(i.e. smallest) being uppermost in the zooid, and this could
be evidence of extraembryonic nutrition. Prouho tended to
believe that self-fertilisation was the rule among bryozoans,
since in those species in which he recorded sexual products,
they often matured simultaneously. He observed that spermatozoids were concentrated around the ovary in
Alcyonidium albidum , but admitted that male and female
gonads began their formation non-simultaneously in some
zooids in A . duplex , and that if cross-fertilisation existed it
should happen during the egg’s passage through the intertentacular organ. Finally, he rejected the idea that alien sperm
could enter the zooid cavity using the same organ, since the
activity of its cilia was directed towards the outside.
Braem ( 1896 ) confi rmed Allman’s ( 1856 ) fi ndings on the
position of the gonad in the freshwater ctenostome
Paludicella articulata (as P . ehrenbergi ). He specifi ed that
the male gonad was paired, described vitellogenesis and
made egg measurements. He documented that released eggs
were surrounded by a fertilization envelope and sometimes
stuck to the maternal colony. In his later papers Braem
( 1908a , b ) briefl y described the structure of spermatozoids
and made measurements of them in the ctenostomes
Paludicella sp. [ P . articulata ] and Triticella sp.
Waters ( 1896a [1898] ) discovered the external
membranous brooding sacs (which he termed ovicells) of
Appendices
stomes, noting that it is accompanied by strong compression
of the egg and occurs when the polypide degenerates; up
until now, Gerwerzhagen ( 1913 ) had been thought to be the
fi rst to describe this phenomenon. Nielsen ( 1981 ) has
described oviposition in Fenestrulina miramara (described
as F . malusii ) as being undertaken by the everted lophophore
and almost without the egg deformation (see also below);
however, Pergen’s ( 1889 ) description is very realistic, and it
is unclear why oviposition is so different in congeneric species. A further important observation was that the ovary continued producing ova during polypide recycling, in accord
with the observations of Van Beneden ( 1844b ) and Vigelius
( 1884a ). Although fi nding only gonochoristic zooids,
Pergens believed that the sex of the zooid could change since
he recorded “spermatosporen” in ovicelled zooids. He also
observed a zygote and two polar bodies in the ovicell.
The classical works of Prouho ( 1889 , 1892 ) revealed different methods of brooding in several ctenostome bryozoans,
as well as demonstrating the presence of both brooding and
non-brooding species within the same ctenostome genus,
Alcyonidium . Non-brooder A. albidum has simultaneously
hermaphrodite zooids, with an ovary developing on the
funiculus and spermatogenic tissue on the cystid wall in the
proximal region. Judging from Prouho illustrations, the
ovary contains up to 18 small oocytes and up to three ovulated eggs occur in the body cavity. Prouho ( 1889 , p. 197)
described the “transparent and … delicate shell” [vitelline
membrane] surrounding the ovulated eggs and observed
their release through the intertentacular organ, proving that it
is an oviduct. He also suggested that fertilization possibly
occurred prior to the appearance of the “shell.”
Using anatomical sections, Prouho investigated the structure of the intertentacular organ in Electra pilosa (as Membranipora ) and Alcyonidium duplex . He observed egg release
through the “genital pore” [supraneural coelomopore] in the
non-brooding ctenostome Hypophorella expansa , thus showing that Ehlers ( 1876 ) was mistaken when he wrote that he
observed an intertentacular organ in the retracted polypides in
this species. Brooding within the introvert was described in
four species: Pherusella tubulosa (as Pherusa ), Flustrellidra
hispida (as Flustrella ), Alcyonidium variegatum and A .
duplex . In three of them the polypide degenerates, and several embryos are brooded simultaneously: 4–5 in the fi rst
two species [there can be up to eight embryos in F . hispida
according to Hayward ( 1985 )], and 6–8 in the third (it is not
clear from Prouho’s description how many embryos are
simultaneously brooded in A . variegatum ). According to his
description, in A . duplex the male germ cells are developed
on the funiculus of the fi rst polypide, at the site of its attachment to the stomach; they then migrate to the body wall,
establishing the gonad. An ovary is formed in the place
where the funiculus of the second polypide (whose bud coexists for some time with the fi rst one) attaches to the body
wall. There are 7–9 (up to 11) oocytes seen in the ovary in
Prouho’s illustrations. The ovulated eggs are irregular in
shape. In contrast with the fi rst polypide, which fi nally
degenerates, the polypide forming the ovary has an intertentacular organ. Released eggs stick to the polypide diaphragm
region [presumably, by their fertilization envelopes], being
withdrawn into the vestibulum during polypide retractions
and exposed when it expands. Later the third polypide forms
a new ovary and has the same structure as the second one that
degenerates. No new testis develops in the zooid.
In three species with a cyphonautes larva ( Electra pilosa ,
A . albidum and H . expansa ) ovulated eggs are of irregular
shape and are said to possess “slow ameboidal movements”
in the zooid cavity (Prouho 1892 , p. 608). They are surrounded by the “vitelline membrane” that was closely
apposed to the oocyte, and the elevation of the fertilization
envelope was described to occur after the passage of the eggs
through the intertentacular organ or supraneural coelomopore. Prouho recorded the subsequent appearance of two
polar bodies in the perivitelline space of recently spawned
zygotes in these species.
In Nolella dilatata (as Cylindroecium dilatatum ) Prouho
found, as he thought, internal brooding. According to his
description and fi gure explanations ( 1892 , pl. 14, fi gs 14–17),
2–3 “eggs” are incubated, adhering to the internal surface of
the zooid wall. Larvae were presumed to leave the zooid coelom through a rupture of this wall. It is also depicted that the
embryos are enlarged during brooding, with the youngest
(i.e. smallest) being uppermost in the zooid, and this could
be evidence of extraembryonic nutrition. Prouho tended to
believe that self-fertilisation was the rule among bryozoans,
since in those species in which he recorded sexual products,
they often matured simultaneously. He observed that spermatozoids were concentrated around the ovary in
Alcyonidium albidum , but admitted that male and female
gonads began their formation non-simultaneously in some
zooids in A . duplex , and that if cross-fertilisation existed it
should happen during the egg’s passage through the intertentacular organ. Finally, he rejected the idea that alien sperm
could enter the zooid cavity using the same organ, since the
activity of its cilia was directed towards the outside.
Braem ( 1896 ) confi rmed Allman’s ( 1856 ) fi ndings on the
position of the gonad in the freshwater ctenostome
Paludicella articulata (as P . ehrenbergi ). He specifi ed that
the male gonad was paired, described vitellogenesis and
made egg measurements. He documented that released eggs
were surrounded by a fertilization envelope and sometimes
stuck to the maternal colony. In his later papers Braem
( 1908a , b ) briefl y described the structure of spermatozoids
and made measurements of them in the ctenostomes
Paludicella sp. [ P . articulata ] and Triticella sp.
Waters ( 1896a [1898] ) discovered the external
membranous brooding sacs (which he termed ovicells) of
Appendices