TllE PIIYSIOI,OOY OF ASUIDIANY
107
therefore particularly interesting that different types of granule bearing
cell should occur in Pleurogona and Enterogona. In the Pleurogona the
goiiads are found on the mantle wall and as ftlr as we know have no
comection with the dorssl cord (vide infra) but in Enterogontl the
gonad is found within tho visceral loop and appears to have the terminal
bulb of the dorsal cord embedded within it. In passing we may note that
Dawson and Hisaw commented that " the best preparations (in
Chelg080m~) were obtained in animals with mature gonads ", ao lending
credence to the idea that there may be some relationship between the
granules and sexual activity. Thiebold and Illoul found similar granules,
stained with aldehyde fuchsin and with Alcian Blue, in the cerebral
cortex of Ciona intestinalis. They located faint traces of similar granules
in fibres of the cerebral medulla thus suggesting axon transport. These
workers also compared their preparations with similar ones from the
bivalve Mgtilus galloprovincialis L. and concluded that the concentration of granular material in the ascidian must be very low in comparison
to the mussel. Similar granules in Ciona intedimlis have also been
found by Chambost (1969). Lane (1968, 1972) conoluded from electron
micrographs that the granules were formed from the Golgi body and
that acid phosphatases werc also present in the cells.
There is thus very clear evidence for the presence of granular material
in cortical cells of the cerebral gtmglion of all species examined but we
have no idea as to what function it may perform, whether it may be the
precursor of a substance transported to axonal terminations, secreted
within the ganglion or whether it may have some other function. There
is indeed nothing at all to prove that they are true neurosecretions.
Clark (1966) has pointed out that all neurones produce a variety of
vesicular secretlions and in advanced animals there may be a high
degree of structural specialization in the nervow system which permits
the neurosecretory system to bc readily identified. In animals with
simple nervous systems this is not so. Clark concludes: " An element of
doubt must therefore remain about all cells with stainable inclusions
that are discovered in the centraI nervous system of primitive animals. "
xrr. THE NEURAL GLAND
A. Structure and cyclic actiuity
The neural wmplex of ascidians consists of the ncrve ganglion
(p. 87) :md ti neural gland 1,ying in the mantle wall betwecm the two
siphons tinct sitrrounded by t i h;wmocoolic Hpaw. In the majority of'
Ltscidians the gsnglion lies dorsdlav to the &rid and closely apponed to
it, but in stolidobranchs the gland ifs dornr~l to the ganglion. Becauw of
107
therefore particularly interesting that different types of granule bearing
cell should occur in Pleurogona and Enterogona. In the Pleurogona the
goiiads are found on the mantle wall and as ftlr as we know have no
comection with the dorssl cord (vide infra) but in Enterogontl the
gonad is found within tho visceral loop and appears to have the terminal
bulb of the dorsal cord embedded within it. In passing we may note that
Dawson and Hisaw commented that " the best preparations (in
Chelg080m~) were obtained in animals with mature gonads ", ao lending
credence to the idea that there may be some relationship between the
granules and sexual activity. Thiebold and Illoul found similar granules,
stained with aldehyde fuchsin and with Alcian Blue, in the cerebral
cortex of Ciona intestinalis. They located faint traces of similar granules
in fibres of the cerebral medulla thus suggesting axon transport. These
workers also compared their preparations with similar ones from the
bivalve Mgtilus galloprovincialis L. and concluded that the concentration of granular material in the ascidian must be very low in comparison
to the mussel. Similar granules in Ciona intedimlis have also been
found by Chambost (1969). Lane (1968, 1972) conoluded from electron
micrographs that the granules were formed from the Golgi body and
that acid phosphatases werc also present in the cells.
There is thus very clear evidence for the presence of granular material
in cortical cells of the cerebral gtmglion of all species examined but we
have no idea as to what function it may perform, whether it may be the
precursor of a substance transported to axonal terminations, secreted
within the ganglion or whether it may have some other function. There
is indeed nothing at all to prove that they are true neurosecretions.
Clark (1966) has pointed out that all neurones produce a variety of
vesicular secretlions and in advanced animals there may be a high
degree of structural specialization in the nervow system which permits
the neurosecretory system to bc readily identified. In animals with
simple nervous systems this is not so. Clark concludes: " An element of
doubt must therefore remain about all cells with stainable inclusions
that are discovered in the centraI nervous system of primitive animals. "
xrr. THE NEURAL GLAND
A. Structure and cyclic actiuity
The neural wmplex of ascidians consists of the ncrve ganglion
(p. 87) :md ti neural gland 1,ying in the mantle wall betwecm the two
siphons tinct sitrrounded by t i h;wmocoolic Hpaw. In the majority of'
Ltscidians the gsnglion lies dorsdlav to the &rid and closely apponed to
it, but in stolidobranchs the gland ifs dornr~l to the ganglion. Becauw of