294
Aetea sica (as A . anguina forma recta ) and an ovary. Later
this mode of brooding was described by a number of authors
(see Sect. 2.4.1 of Chap. 2 ). The ovary is positioned inside
the adnate, horizontal part of the maternal zooid; Waters
noted four young oocytes.
Delage and Hérouard ( 1897 ) briefl y reviewed bryozoan
sexual reproduction in their handbook, but the number of
original papers upon which their account was based were
relatively few.
The monograph of Calvet ( 1900 ) became an important
landmark in the development of knowledge about bryozoan anatomy including the reproductive system. Apart
from the structure of brood chambers in several cheilostome species, he described brooding in the tentacle
sheath in the ctenostomes Bowerbankia pustulosa ,
Amathia lendigera , A. semiconvoluta and Vesicularia spinosa . Calvet discovered the embryophore in the cheilostomes Bugula simplex (as B . sabatieri ) and Cellaria
fi stulosa , but did not understand its signifi cance. He nevertheless noted that the size of the cells in the brood sac
wall correlated with the developmental stage of the
embryo in Cellaria – the more advanced the embryo, the
larger the cells. The intertentacular organs of Electra
pilosa (as Membranipora var. dentata ) and Alcyonidium
cellarioides were studied by anatomical section. Calvet
recorded protandrous zooidal hermaphroditism in ten cheilostome species, and simultaneous zooidal hermaphroditism in
six cheilostomes and two ctenostomes. He stressed that early
zooids did not reproduce sexually. It was mentioned that the
position of the mature ovary is generally constant for the
same species but can be somewhat variable for the whole
group as well as in the same species. In the majority of the
species studied the ovary is placed “parietally” [on the zooid
wall, mainly basally], although it could be suspended on
funicular strands or attached to the polypide, explaining
existing controversies to some extent (see above). Male
gonads were recorded on the lateral and basal walls in the
proximal region of the cystid.
Dividing bryozoans into oviparous and viviparous types,
Calvet showed the striking difference in egg number among
ovaries – oviparous bryozoans have many more oocytes. In
viviparous species the eggs are often pictured in pairs
[oocyte doublets], some of them degenerating inside the
ovary [mature nurse cells]. It is clearly seen from the illustrations that cheilostomes, except for Electra species (as
Membranipora ), possess fewer eggs in the ovary than the
ctenostomes studied. Calvet observed spermatogenesis in
23 species (19 cheilostomes, two ctenostomes and two
cyclostomes), illustrating in detail different stages of spermatozoid development in Bugula simplex and Cryptosula
pallasiana , and stating that the initial “cellule spermatoblastique” originated from mesenchymatous tissue in young
zooidal buds. This researcher also recorded clusters of
spermatozoids [spermatozeugmata] in Electra pilosa and
described their disaggregation.
Calvet carefully investigated ovarian structure, oogenesis
and spermatogenesis in simultaneously hermaphrodite
zooids of B . simplex , resolving several important problems.
According to his observations, the position of the ovary varies
in this species. The fully formed ovary is either attached to the
peritoneal lining of the zooid wall or stomach or suspended
on funicular strands in the zooid cavity. He mentioned the
rare occurrence of two ovaries in some zooids. In one instance
he depicted an ovary resting on the zooid wall (pl. 3, fi g. 14)
and, additionally, “cellules ovulaires” inside the funiculus in
the same zooid. An important conclusion was that, wherever
it is positioned, the ovary is always “associated with the mesenchymatous tissue,” and its cells “come directly, and by
simple differentiation, from” it (pp. 75, 295), according with
the statements of Ostroumoff ( 1886a , b ) and Vigelius ( 1886 ).
However, in contrast with the fi ndings of the latter author,
Calvet found early female cells “free” in the cavity of zooid
buds containing a developing polypide. In zooids with polypides at a more advanced stage, these cells were then either
found within the polypide peritoneum or the peritoneum of
the cystid wall or suspended on funicular strands (see also
Joliet 1877a ). Calvet stated that female cells were also incidentally found in terminal zooids with developed polypides,
specifi cally within the funicular tissue or peritoneal lining. He
criticized the opinion of earlier authors, for instance Nitsche
( 1869 ), concerning the origination of the ovary from the
“endocyst”. Actually, Nitsche, who did not use thin sectioning, was unable to detect the peritoneum of the cystid wall.
According to Calvet’s observations on oviparous species,
ova within ovaries are surrounded by a few fl attened cells
whereas in viviparous species the ovary wall constitutes both
fl attened (“membrane folliculaire”) and cylindrical cells
forming either a narrow (pedunculate) or wide basal part that
connects the ovary to the cystid wall. It is clear from his illustrations that Calvet saw basal cells in some ovaries too. A
unusual type of ovary, developing on the caecum and partially the funiculus, was described in the ctenostome Nolella
dilatata (as Cylindroecium dilatatum ). Calvet could not distinguish any accessory cells in it, only numerous small eggs.
He described the development of the ovary and accompanying changes in female cell structure. According to his
description, following their differentiation, the early “cellules ovulaires” are further enveloped by multiplying mesenchymatous cells in different species of Bugula and in the
ctenostome Bowerbankia pustulosa . In all but one of the
other bryozoans studied, the process is said to be different.
Following differentiation from the “mesenchymatous elements”, the female germ cells that differ from all others in
having a bubble-like shape, more intense staining and a
larger diameter, each divide once. Judging from his fi gures,
Calvet may have seen 2–4 oogonia (“cellules ovariennes
Appendices
Aetea sica (as A . anguina forma recta ) and an ovary. Later
this mode of brooding was described by a number of authors
(see Sect. 2.4.1 of Chap. 2 ). The ovary is positioned inside
the adnate, horizontal part of the maternal zooid; Waters
noted four young oocytes.
Delage and Hérouard ( 1897 ) briefl y reviewed bryozoan
sexual reproduction in their handbook, but the number of
original papers upon which their account was based were
relatively few.
The monograph of Calvet ( 1900 ) became an important
landmark in the development of knowledge about bryozoan anatomy including the reproductive system. Apart
from the structure of brood chambers in several cheilostome species, he described brooding in the tentacle
sheath in the ctenostomes Bowerbankia pustulosa ,
Amathia lendigera , A. semiconvoluta and Vesicularia spinosa . Calvet discovered the embryophore in the cheilostomes Bugula simplex (as B . sabatieri ) and Cellaria
fi stulosa , but did not understand its signifi cance. He nevertheless noted that the size of the cells in the brood sac
wall correlated with the developmental stage of the
embryo in Cellaria – the more advanced the embryo, the
larger the cells. The intertentacular organs of Electra
pilosa (as Membranipora var. dentata ) and Alcyonidium
cellarioides were studied by anatomical section. Calvet
recorded protandrous zooidal hermaphroditism in ten cheilostome species, and simultaneous zooidal hermaphroditism in
six cheilostomes and two ctenostomes. He stressed that early
zooids did not reproduce sexually. It was mentioned that the
position of the mature ovary is generally constant for the
same species but can be somewhat variable for the whole
group as well as in the same species. In the majority of the
species studied the ovary is placed “parietally” [on the zooid
wall, mainly basally], although it could be suspended on
funicular strands or attached to the polypide, explaining
existing controversies to some extent (see above). Male
gonads were recorded on the lateral and basal walls in the
proximal region of the cystid.
Dividing bryozoans into oviparous and viviparous types,
Calvet showed the striking difference in egg number among
ovaries – oviparous bryozoans have many more oocytes. In
viviparous species the eggs are often pictured in pairs
[oocyte doublets], some of them degenerating inside the
ovary [mature nurse cells]. It is clearly seen from the illustrations that cheilostomes, except for Electra species (as
Membranipora ), possess fewer eggs in the ovary than the
ctenostomes studied. Calvet observed spermatogenesis in
23 species (19 cheilostomes, two ctenostomes and two
cyclostomes), illustrating in detail different stages of spermatozoid development in Bugula simplex and Cryptosula
pallasiana , and stating that the initial “cellule spermatoblastique” originated from mesenchymatous tissue in young
zooidal buds. This researcher also recorded clusters of
spermatozoids [spermatozeugmata] in Electra pilosa and
described their disaggregation.
Calvet carefully investigated ovarian structure, oogenesis
and spermatogenesis in simultaneously hermaphrodite
zooids of B . simplex , resolving several important problems.
According to his observations, the position of the ovary varies
in this species. The fully formed ovary is either attached to the
peritoneal lining of the zooid wall or stomach or suspended
on funicular strands in the zooid cavity. He mentioned the
rare occurrence of two ovaries in some zooids. In one instance
he depicted an ovary resting on the zooid wall (pl. 3, fi g. 14)
and, additionally, “cellules ovulaires” inside the funiculus in
the same zooid. An important conclusion was that, wherever
it is positioned, the ovary is always “associated with the mesenchymatous tissue,” and its cells “come directly, and by
simple differentiation, from” it (pp. 75, 295), according with
the statements of Ostroumoff ( 1886a , b ) and Vigelius ( 1886 ).
However, in contrast with the fi ndings of the latter author,
Calvet found early female cells “free” in the cavity of zooid
buds containing a developing polypide. In zooids with polypides at a more advanced stage, these cells were then either
found within the polypide peritoneum or the peritoneum of
the cystid wall or suspended on funicular strands (see also
Joliet 1877a ). Calvet stated that female cells were also incidentally found in terminal zooids with developed polypides,
specifi cally within the funicular tissue or peritoneal lining. He
criticized the opinion of earlier authors, for instance Nitsche
( 1869 ), concerning the origination of the ovary from the
“endocyst”. Actually, Nitsche, who did not use thin sectioning, was unable to detect the peritoneum of the cystid wall.
According to Calvet’s observations on oviparous species,
ova within ovaries are surrounded by a few fl attened cells
whereas in viviparous species the ovary wall constitutes both
fl attened (“membrane folliculaire”) and cylindrical cells
forming either a narrow (pedunculate) or wide basal part that
connects the ovary to the cystid wall. It is clear from his illustrations that Calvet saw basal cells in some ovaries too. A
unusual type of ovary, developing on the caecum and partially the funiculus, was described in the ctenostome Nolella
dilatata (as Cylindroecium dilatatum ). Calvet could not distinguish any accessory cells in it, only numerous small eggs.
He described the development of the ovary and accompanying changes in female cell structure. According to his
description, following their differentiation, the early “cellules ovulaires” are further enveloped by multiplying mesenchymatous cells in different species of Bugula and in the
ctenostome Bowerbankia pustulosa . In all but one of the
other bryozoans studied, the process is said to be different.
Following differentiation from the “mesenchymatous elements”, the female germ cells that differ from all others in
having a bubble-like shape, more intense staining and a
larger diameter, each divide once. Judging from his fi gures,
Calvet may have seen 2–4 oogonia (“cellules ovariennes
Appendices