120
Harmer ( 1926 , 1934 , 1957 ) considered ovicell structure in
all three cheilostome volumes of his famous monograph “The
Polyzoa of the Siboga Expedition”. In the 1926 volume he
used slightly modifi ed schematics of endozooidal and hyperstomial ovicells (fi g. 1A–C) published by Calvet ( 1900 ).
Harmer also modifi ed Levinsen’s ( 1902 , 1909 ) spelling of
“ectoooecium” and “endoooecium” to “ectooecium” and
“entooecium”, and used “entozooecial ovicells” instead of
“endozooecial”. In the final “Siboga” volume Harmer,
following Levinsen ( 1909 ), depicted three schemes of
ovicell structure, with ooecia consisting of two external
non- calcifi ed walls (ecto- and entooecium) and a double
inner wall (cryptocyst) between (Harmer 1957 , fi g. 15B–D).
In all cases, ooecial walls were depicted as a continuation of
the daughter-zooid frontal wall.
Interestingly, when using Calvet’s ( 1900 , fi g. 10) schema
for Bugula , Harmer ( 1926 , fi g. 1C) for some reason did not
mention or illustrate the communication pore of the ooecium
(the same omission was made by Levinsen in his 1909
monograph, see above). It is all the more strange since he
discussed Calvet’s fi nding in an earlier work (Harmer
1902 , p. 284) and stressed that “the vestigial … ovicell is …
defi nitely shown to be a derivative of the distal zooecium” in
B . longicauda (Harmer 1926 , p. 451). Marcus ( 1926 , fi g. 19,
1940 , fi g. 54), on the other hand, depicted this pore, using
the modifi ed schema of B . avicularia from the work of
Gerwerzhagen ( 1913 , textfi g. 1).
Contrary to all previous authors, Cori ( 1941 , fi g. 343)
modifi ed the scheme of Calvet ( 1900 , fi g. 10) and pictured
communication between ooecial and maternal-zooid coeloms instead. The reason for this is unclear, since Cori did
not himself make sections of ovicells. It is quite possible that
he was infl uenced by the opinions of earlier authors such as
Nitsche ( 1869 ), Vigelius ( 1884a , 1886 ), and Delage and
Hérouard ( 1897 ).
Cori’s fi gure was approved by Silén ( 1944 , 1945 ), however.
It should be noted that Silén was probably the fi rst to realize
the importance of the communication between coelomic
cavities (instead of a continuity of zooidal walls) in regard to
ooecial origins. Based on histological sections, Silén ( 1944 ,
fi gs. 18–19) reconstructed ovicell anatomy in Scrupocellaria
scabra (Fig. 2.4 ), and described the ooecial coelom as confl uent with that of the maternal autozooid.
Silén ( 1945 ) then published his very infl uential paper,
“The main features of the development of the ovum, embryo
and ooecium in the ooeciferous Bryozoa Gymnolaemata.”
This prominent study dealt with many aspects of bryozoan
structure and reproductive biology, including the development and structure of the ooecia of three cheilostomes:
Callopora dumerilii , Escharella immersa and Fenestrulina
malusii . In this paper Silén refuted the view of earlier
researchers concerning the existence of a connection between
the ooecial coelom and the perigastric cavity of the distal
zooid. Based on sections of Scrupocellaria scabra (see Silén
1944 ) he stated that in all three species studied an ooecial
fold originates from the maternal zooid, the cavity of which
communicates with that of the fold. He showed that the
ooecium starts to develop when the fi rst oocyte begins to
grow in the ovary, and this was suggested as being regulated
by hormones. Silén apparently implied that if ovicellogenesis was triggered by the maternal zooid (its ovary), the ooecium was formed at its expense as well. He obviously
overlooked Calvet’s ( 1900 ) fi nding of the communication
pore in Bugula simplex , unjustly and rather aggressively
criti cizing him for not “understanding of the nature of the”
ooecium, and considering his anatomical schemes of the
ovicells of Amphiblestrum fl emingi and Securifl ustra securifrons as “misapprehended” or “entirely wrong” (Silén 1945 ,
pp. 12–13, see also Ryland 1976 for discussion). Admitting
the correctness of the Levinsen’s data on ooecial development, Silén criticized his view on the connection between the
ooecium and ooecium-producing zooid. The illustrations of
Levinsen clearly showing the origin of the ooecium from
the daughter zooid were considered wrong or were ignored
(for instance, for S . scabra , see 1893 , tab. 1, fi g. 8, 1894 ,
tab. 1, fi g. 22; for E . immersa , see 1909 , pl. 17, fi g. 3a; for
C . aurita , see 1909 , pl. 24, fi g. 16; for Tegella unicornis
(as Membranipora ), see 1893 , tab. 2, fi g. 24; 1894 , tab. 4,
fi g. 19). The earliest stage of ovicellogenesis was described
as “a fl at and narrow prominence from the frontal part of
distal wall [of the mother zooid] … composed of two separate
knobs” (Silén 1945 , p. 9; see also Ryland 1979 ). In accord
with Nitsche ( 1869 ), the external wall of the ooecial fold was
said to be calcifi ed whereas the inner one was membranous.
Finally, Silén extrapolated these statements to all bryozoans
with hyperstomial and endozooidal ovicells (for review and
discussion see also Woollacott and Zimmer 1972a ). It is
noteworthy that in his previous paper Silén ( 1944 , captions
for text-fi gs. 20–24) wrote that the ooecium is formed by the
distal zooid in endozooidal ovicells.
Silén’s view that the ooecium originates from the maternal
zooid was infl uenced by Harmer ( 1902 ), who suggested
that the ooecium originated from the two oral spines in the
cribrimorph Euthyroides episcopalis (discussed in Ostrovsky
1998 , see also above). Based on this, and his own inferences
concerning the evolution of spines in Gymnolaemata, Silén
( 1942 , 1945 , p. 17) speculated that the ooecium “is possibly
a structure composed of transformed zoid-buds”.
Silén’s ( 1945 ) study was so comprehensive, and his
arguments so convincing, that they have been accepted or
mentioned by the authors of most large reviews and handbooks on Bryozoa up to the present time (Brown 1952 ;
Hyman 1959 ; Brien 1960 ; Larwood 1962 ; Prenant and
Bobin 1966 ; Powell 1967 ; Ryland 1970 , 1976 , 1979 ; Kluge
1975 ; Ryland and Hayward 1977 ; Ström 1977 ; Hayward
and Ryland 1979 , 1998 , 1999 ; Reed 1991 ; Viskova 1992 ;
2 Cheilostome Brood Chambers: Structure, Formation, Evolution
Harmer ( 1926 , 1934 , 1957 ) considered ovicell structure in
all three cheilostome volumes of his famous monograph “The
Polyzoa of the Siboga Expedition”. In the 1926 volume he
used slightly modifi ed schematics of endozooidal and hyperstomial ovicells (fi g. 1A–C) published by Calvet ( 1900 ).
Harmer also modifi ed Levinsen’s ( 1902 , 1909 ) spelling of
“ectoooecium” and “endoooecium” to “ectooecium” and
“entooecium”, and used “entozooecial ovicells” instead of
“endozooecial”. In the final “Siboga” volume Harmer,
following Levinsen ( 1909 ), depicted three schemes of
ovicell structure, with ooecia consisting of two external
non- calcifi ed walls (ecto- and entooecium) and a double
inner wall (cryptocyst) between (Harmer 1957 , fi g. 15B–D).
In all cases, ooecial walls were depicted as a continuation of
the daughter-zooid frontal wall.
Interestingly, when using Calvet’s ( 1900 , fi g. 10) schema
for Bugula , Harmer ( 1926 , fi g. 1C) for some reason did not
mention or illustrate the communication pore of the ooecium
(the same omission was made by Levinsen in his 1909
monograph, see above). It is all the more strange since he
discussed Calvet’s fi nding in an earlier work (Harmer
1902 , p. 284) and stressed that “the vestigial … ovicell is …
defi nitely shown to be a derivative of the distal zooecium” in
B . longicauda (Harmer 1926 , p. 451). Marcus ( 1926 , fi g. 19,
1940 , fi g. 54), on the other hand, depicted this pore, using
the modifi ed schema of B . avicularia from the work of
Gerwerzhagen ( 1913 , textfi g. 1).
Contrary to all previous authors, Cori ( 1941 , fi g. 343)
modifi ed the scheme of Calvet ( 1900 , fi g. 10) and pictured
communication between ooecial and maternal-zooid coeloms instead. The reason for this is unclear, since Cori did
not himself make sections of ovicells. It is quite possible that
he was infl uenced by the opinions of earlier authors such as
Nitsche ( 1869 ), Vigelius ( 1884a , 1886 ), and Delage and
Hérouard ( 1897 ).
Cori’s fi gure was approved by Silén ( 1944 , 1945 ), however.
It should be noted that Silén was probably the fi rst to realize
the importance of the communication between coelomic
cavities (instead of a continuity of zooidal walls) in regard to
ooecial origins. Based on histological sections, Silén ( 1944 ,
fi gs. 18–19) reconstructed ovicell anatomy in Scrupocellaria
scabra (Fig. 2.4 ), and described the ooecial coelom as confl uent with that of the maternal autozooid.
Silén ( 1945 ) then published his very infl uential paper,
“The main features of the development of the ovum, embryo
and ooecium in the ooeciferous Bryozoa Gymnolaemata.”
This prominent study dealt with many aspects of bryozoan
structure and reproductive biology, including the development and structure of the ooecia of three cheilostomes:
Callopora dumerilii , Escharella immersa and Fenestrulina
malusii . In this paper Silén refuted the view of earlier
researchers concerning the existence of a connection between
the ooecial coelom and the perigastric cavity of the distal
zooid. Based on sections of Scrupocellaria scabra (see Silén
1944 ) he stated that in all three species studied an ooecial
fold originates from the maternal zooid, the cavity of which
communicates with that of the fold. He showed that the
ooecium starts to develop when the fi rst oocyte begins to
grow in the ovary, and this was suggested as being regulated
by hormones. Silén apparently implied that if ovicellogenesis was triggered by the maternal zooid (its ovary), the ooecium was formed at its expense as well. He obviously
overlooked Calvet’s ( 1900 ) fi nding of the communication
pore in Bugula simplex , unjustly and rather aggressively
criti cizing him for not “understanding of the nature of the”
ooecium, and considering his anatomical schemes of the
ovicells of Amphiblestrum fl emingi and Securifl ustra securifrons as “misapprehended” or “entirely wrong” (Silén 1945 ,
pp. 12–13, see also Ryland 1976 for discussion). Admitting
the correctness of the Levinsen’s data on ooecial development, Silén criticized his view on the connection between the
ooecium and ooecium-producing zooid. The illustrations of
Levinsen clearly showing the origin of the ooecium from
the daughter zooid were considered wrong or were ignored
(for instance, for S . scabra , see 1893 , tab. 1, fi g. 8, 1894 ,
tab. 1, fi g. 22; for E . immersa , see 1909 , pl. 17, fi g. 3a; for
C . aurita , see 1909 , pl. 24, fi g. 16; for Tegella unicornis
(as Membranipora ), see 1893 , tab. 2, fi g. 24; 1894 , tab. 4,
fi g. 19). The earliest stage of ovicellogenesis was described
as “a fl at and narrow prominence from the frontal part of
distal wall [of the mother zooid] … composed of two separate
knobs” (Silén 1945 , p. 9; see also Ryland 1979 ). In accord
with Nitsche ( 1869 ), the external wall of the ooecial fold was
said to be calcifi ed whereas the inner one was membranous.
Finally, Silén extrapolated these statements to all bryozoans
with hyperstomial and endozooidal ovicells (for review and
discussion see also Woollacott and Zimmer 1972a ). It is
noteworthy that in his previous paper Silén ( 1944 , captions
for text-fi gs. 20–24) wrote that the ooecium is formed by the
distal zooid in endozooidal ovicells.
Silén’s view that the ooecium originates from the maternal
zooid was infl uenced by Harmer ( 1902 ), who suggested
that the ooecium originated from the two oral spines in the
cribrimorph Euthyroides episcopalis (discussed in Ostrovsky
1998 , see also above). Based on this, and his own inferences
concerning the evolution of spines in Gymnolaemata, Silén
( 1942 , 1945 , p. 17) speculated that the ooecium “is possibly
a structure composed of transformed zoid-buds”.
Silén’s ( 1945 ) study was so comprehensive, and his
arguments so convincing, that they have been accepted or
mentioned by the authors of most large reviews and handbooks on Bryozoa up to the present time (Brown 1952 ;
Hyman 1959 ; Brien 1960 ; Larwood 1962 ; Prenant and
Bobin 1966 ; Powell 1967 ; Ryland 1970 , 1976 , 1979 ; Kluge
1975 ; Ryland and Hayward 1977 ; Ström 1977 ; Hayward
and Ryland 1979 , 1998 , 1999 ; Reed 1991 ; Viskova 1992 ;
2 Cheilostome Brood Chambers: Structure, Formation, Evolution