xpecitneris of Cionct intea/inaZix and Aros and Konok (1969) hare redescribed the ceiitriil ganglion of C. intestinuZi.s. The following account
of thc nervous snatorny is based upon the findings of these authors
amongst whom tlierr is general agrecmetit.
There is only one ganglion in the adult ascidian and this is situated
in the dorsal mantle wall inid-way between the two siphons and
adjacent to thc neural gland (Fig. 25). The ganglion may measure as
much ~n 3 min in length in an adult Ciona. It is surrounded by a
cionnective tissue sheath and has main nerve fibres arising at either
end. Millur and Hilton both describe also somc very fine fibres arising
at, the pcriphrry of the ganglion tmd apparently innervating the
musculature iii the surrounding mantle tissues.
Thc internal structure of the ganglion is tjrpicul of that found in
most invertebrates with tm outer cellular cortex and a fibrous medulla.
Within the centre there are two sizes of neuron, large ones which
rwcording to Millar are (3 p x 18 p and small ones measuring between
5-26 p and (i p in diiimet,er. Millar ancl Arm ancl Konok considered that
iill of thew cclls are unipolar hut Hilton believed that as well as the
iinipolar cc4ls therv are a few multipolar ones. Aros and Konok also
rtvorded the prescwcc of glial cells in the cortex and several authors
(see below) have clescribed " neuroserretory " granule-laden cells in the
cortex. Hilton and Millar both described the presence of minute
fibrillac in the neurons but it is not certain whcther this was a misinterpretation of the nature of the granular " neurosecretory " cells.
The centriil medullary region of the ganglion is composed of a dense
irggregation of nerve fibres mostly oriented along the length of the
ganglion. Thc axom arising from the cortical neurons enter the medulla
rind turn iilong its length although ct few may cross it diagonally so as
to emerge in nerves on the opposite side, and some appear only to be
fibres of association neurons within the ganglion. Millar also mentions
the presenre of t i few sniall multipolar cclls in the medulla while Aroe
and Konok indirate the presence of glid cells in this region. Within the
iwiiropile Dilly (1 96%) has described polarized synaptic junctions in
wltieh vcbsicles of two different sizes occur adjacent to the pre-synaptic
membrane ; grannles occur in soinch of the large vesicles. The Bignifioance
of these two typw of vesicle is not known but Dilly suggeHt8 that they
may releassc different tranclmittor suhtanccs which perform Heparatt:
funrtions or that one is potentirLted hy the other. Alternatively there
may be an intimate association between normal synaptic transmission
and neurosecretion ; granule bearing vesicles assumed to have a neurosecretory function occur in the peripheral neurons of the ganglion
(see p. 100) but until a great deal more is known about these and the
of thc nervous snatorny is based upon the findings of these authors
amongst whom tlierr is general agrecmetit.
There is only one ganglion in the adult ascidian and this is situated
in the dorsal mantle wall inid-way between the two siphons and
adjacent to thc neural gland (Fig. 25). The ganglion may measure as
much ~n 3 min in length in an adult Ciona. It is surrounded by a
cionnective tissue sheath and has main nerve fibres arising at either
end. Millur and Hilton both describe also somc very fine fibres arising
at, the pcriphrry of the ganglion tmd apparently innervating the
musculature iii the surrounding mantle tissues.
Thc internal structure of the ganglion is tjrpicul of that found in
most invertebrates with tm outer cellular cortex and a fibrous medulla.
Within the centre there are two sizes of neuron, large ones which
rwcording to Millar are (3 p x 18 p and small ones measuring between
5-26 p and (i p in diiimet,er. Millar ancl Arm ancl Konok considered that
iill of thew cclls are unipolar hut Hilton believed that as well as the
iinipolar cc4ls therv are a few multipolar ones. Aros and Konok also
rtvorded the prescwcc of glial cells in the cortex and several authors
(see below) have clescribed " neuroserretory " granule-laden cells in the
cortex. Hilton and Millar both described the presence of minute
fibrillac in the neurons but it is not certain whcther this was a misinterpretation of the nature of the granular " neurosecretory " cells.
The centriil medullary region of the ganglion is composed of a dense
irggregation of nerve fibres mostly oriented along the length of the
ganglion. Thc axom arising from the cortical neurons enter the medulla
rind turn iilong its length although ct few may cross it diagonally so as
to emerge in nerves on the opposite side, and some appear only to be
fibres of association neurons within the ganglion. Millar also mentions
the presenre of t i few sniall multipolar cclls in the medulla while Aroe
and Konok indirate the presence of glid cells in this region. Within the
iwiiropile Dilly (1 96%) has described polarized synaptic junctions in
wltieh vcbsicles of two different sizes occur adjacent to the pre-synaptic
membrane ; grannles occur in soinch of the large vesicles. The Bignifioance
of these two typw of vesicle is not known but Dilly suggeHt8 that they
may releassc different tranclmittor suhtanccs which perform Heparatt:
funrtions or that one is potentirLted hy the other. Alternatively there
may be an intimate association between normal synaptic transmission
and neurosecretion ; granule bearing vesicles assumed to have a neurosecretory function occur in the peripheral neurons of the ganglion
(see p. 100) but until a great deal more is known about these and the