TIlE PIlYRIOLOOY OF ARCIDIANS
125
that i t rnigtit lw wdocriiv. in function, pcbrhaps associated with long
term metabolic activity or gonadial cycles rather than with the daily
life of the aninicil. In this context we may recall the experiments of
Carlisle (1951) in which he inject>c*d gonadotrophin into ascidians and
stimulated gamete release. When he cut the visceral nerve this response
was destroyed, but in cutting the visceral nerve he would almost
certainly have also cut the dorsal strand so that we do not know whether
the response might have been mediated through the visceral nerve or
the dorsal strand. Bouchard-Madrelle (1 967) reported that oogenesis
is under the control of the neural complex in Cionu intestinalia and if
this is removed, the number of germinal centres decreases and the
young oocytes degenerate. The n limber of oocytes in perivitellogenesis
and that of rnstrire follicles also decrease. Removal of all or a part of
the neural complex suggeated that the neural gland controls the number
of young ooeytes and the germiniil centres while the ganglion controls
the number of mature follicles and oocytes in perivitellogenesis.
There is no indicthtion as to how siich control may be mediated, but it
is possible for the control of‘oogenesis to be by way of the dorsal strand.
However, if that, is the case in Ciona, it is still not clear how m y
mediation miLy oc-cur in pleurogonid forms where the dorsal strand is
not in direct contact with the gonad.
The ontogeny of the dorsal strand and its close association with the
surrounding viscwal fibre complex (p. 91) make it mem more likely
that the strand hna a functional relationship with the visceral nervous
system than with reproductive vycles or other metabolic processes.
The strand and sarrounding fibrvs run along the dorsal side of the
branchial sac arid Fedele (1027, 1938) considered that the fibre complex
was associated with nervous control of ciliary activity in the branchial
stigmata. Recently Mackie et nl. (1974) have described nerve fibres
going from the fibre complex to the ciliated cells of the stigmata in
Ciwella (p. 91). Thus while it is rewonable to associate ciliary activity
with the visceral fibre complex the role of the dorsal strand ibelf
remuins iinexplainetl. Fedele’s (1 038) suggestion that the dona1 strand
is the site of continuing neuroblastogenesis (p. 124) has not been confirmed by other workers, but nevertheless the close association between
fibre complex and strand makes s o m ~ functional reletionship appear
likely. Fedele’s careful observations on the nervous system of ascidiam
have been neglected by many authors and deserve clowr attention ; hi8
suggestion of rontin uing neurobltistogcnesis may warrant re-examination. Alternatively, the strand may perform a nutritive function in
relation to the surrounding nerve cclls and fibres much &IJ glial cell8 do
in the nervous systems of other animals.
125
that i t rnigtit lw wdocriiv. in function, pcbrhaps associated with long
term metabolic activity or gonadial cycles rather than with the daily
life of the aninicil. In this context we may recall the experiments of
Carlisle (1951) in which he inject>c*d gonadotrophin into ascidians and
stimulated gamete release. When he cut the visceral nerve this response
was destroyed, but in cutting the visceral nerve he would almost
certainly have also cut the dorsal strand so that we do not know whether
the response might have been mediated through the visceral nerve or
the dorsal strand. Bouchard-Madrelle (1 967) reported that oogenesis
is under the control of the neural complex in Cionu intestinalia and if
this is removed, the number of germinal centres decreases and the
young oocytes degenerate. The n limber of oocytes in perivitellogenesis
and that of rnstrire follicles also decrease. Removal of all or a part of
the neural complex suggeated that the neural gland controls the number
of young ooeytes and the germiniil centres while the ganglion controls
the number of mature follicles and oocytes in perivitellogenesis.
There is no indicthtion as to how siich control may be mediated, but it
is possible for the control of‘oogenesis to be by way of the dorsal strand.
However, if that, is the case in Ciona, it is still not clear how m y
mediation miLy oc-cur in pleurogonid forms where the dorsal strand is
not in direct contact with the gonad.
The ontogeny of the dorsal strand and its close association with the
surrounding viscwal fibre complex (p. 91) make it mem more likely
that the strand hna a functional relationship with the visceral nervous
system than with reproductive vycles or other metabolic processes.
The strand and sarrounding fibrvs run along the dorsal side of the
branchial sac arid Fedele (1027, 1938) considered that the fibre complex
was associated with nervous control of ciliary activity in the branchial
stigmata. Recently Mackie et nl. (1974) have described nerve fibres
going from the fibre complex to the ciliated cells of the stigmata in
Ciwella (p. 91). Thus while it is rewonable to associate ciliary activity
with the visceral fibre complex the role of the dorsal strand ibelf
remuins iinexplainetl. Fedele’s (1 038) suggestion that the dona1 strand
is the site of continuing neuroblastogenesis (p. 124) has not been confirmed by other workers, but nevertheless the close association between
fibre complex and strand makes s o m ~ functional reletionship appear
likely. Fedele’s careful observations on the nervous system of ascidiam
have been neglected by many authors and deserve clowr attention ; hi8
suggestion of rontin uing neurobltistogcnesis may warrant re-examination. Alternatively, the strand may perform a nutritive function in
relation to the surrounding nerve cclls and fibres much &IJ glial cell8 do
in the nervous systems of other animals.