94
IVAN GOODBODY
described mult(ipo1iw nerve cells throughout the test. In the same paper
hc suggent,od that the epithelitd oells surrounding the vasciilar ampullae
of' the test arc' tactile rweptors innervated by these fibres. However,
cortsidcring thc nature of thc test and its formation, it is unlikely that
nerve cells or receptor ovlls are present in it. I)as used methylene blue
staining to observe these structures but this is an exceedingly difficult
technique with which to demonstrate nervous elements in ascidians and
is likely to stain other structures as well. Hecht (1918b), who made a
careful study of Awidia nigra, was uncertain about the presence of
receptors in the test and considered that responses to stimulation of the
test are due to mechanical transmission through the test to receptors in
thtx siphonul region, a viewpoint also supported by Fedele (1923a).
However, the experinicmts of' Hoyle ( 1952) who stimulated the text
electricdly suggest that there tnuy be some scnsory innervation in the
test, but the innarvat,ion need not include the cell body. Fedele (1923a)
and Millltr (1 953a) have deswibed pear-shaped epithelial sense cells
Burrounded by a numher of supporting cells; each sense cell has a
vacuolc and a distal process which penetrates through the test subetance and a nerve fibre leads away from the narrow end of the cell.
Bone (1959) has deswibed similar cells in pelagic tunicates and suggests
that they are epithelial sensory cells characteristic of tunicates in
general. Fedele and hfillar both found these cells in Ciona intestinulis
to be concentrated on the inside and outside of the siphonal margins and
elsewhere to a lesser extent. Cc4ls of this sort could account for all of the
simple responAes of ascidians outlined below, but whether different
groups of cells have different physiological characteristics and responses
must await, the refinement of techniques for studying them.
The rpithelial sense cells described above are probably the primary
receptor cells of ascidians but two other types of specialized structures
have been reported. These are cupula organs and ocelli. Cupula organs
are described by Fedele ( I 923a) and Millar (1953a) in Ciona inteatinaliv
as dome-shaped evagiriations arising from the mantle wall just inside
the atrial siphon (Fig. 26c). The dome consists of several ordinary sense
cells surrounded by supporting cells and the whole thing covered by test
material which is drawn out at the apex into a long process or flag.
This is the only part of the inner mantle wall where the power of test
secretion has been retained. Similar structures are known from pelagic
tunicates (Fedele, 1923c ; Bonc, 1959) but their function remains
obscure. Thc mantle cavity is ooncerncd with two principal types (Jf
response. It must respond to the presenc-e of faecw so as to eject them
through the atrial siphoii : thin is a simple rctflex action which hardly
requires such specialized structures as the cwpuh organs. The mantle
IVAN GOODBODY
described mult(ipo1iw nerve cells throughout the test. In the same paper
hc suggent,od that the epithelitd oells surrounding the vasciilar ampullae
of' the test arc' tactile rweptors innervated by these fibres. However,
cortsidcring thc nature of thc test and its formation, it is unlikely that
nerve cells or receptor ovlls are present in it. I)as used methylene blue
staining to observe these structures but this is an exceedingly difficult
technique with which to demonstrate nervous elements in ascidians and
is likely to stain other structures as well. Hecht (1918b), who made a
careful study of Awidia nigra, was uncertain about the presence of
receptors in the test and considered that responses to stimulation of the
test are due to mechanical transmission through the test to receptors in
thtx siphonul region, a viewpoint also supported by Fedele (1923a).
However, the experinicmts of' Hoyle ( 1952) who stimulated the text
electricdly suggest that there tnuy be some scnsory innervation in the
test, but the innarvat,ion need not include the cell body. Fedele (1923a)
and Millltr (1 953a) have deswibed pear-shaped epithelial sense cells
Burrounded by a numher of supporting cells; each sense cell has a
vacuolc and a distal process which penetrates through the test subetance and a nerve fibre leads away from the narrow end of the cell.
Bone (1959) has deswibed similar cells in pelagic tunicates and suggests
that they are epithelial sensory cells characteristic of tunicates in
general. Fedele and hfillar both found these cells in Ciona intestinulis
to be concentrated on the inside and outside of the siphonal margins and
elsewhere to a lesser extent. Cc4ls of this sort could account for all of the
simple responAes of ascidians outlined below, but whether different
groups of cells have different physiological characteristics and responses
must await, the refinement of techniques for studying them.
The rpithelial sense cells described above are probably the primary
receptor cells of ascidians but two other types of specialized structures
have been reported. These are cupula organs and ocelli. Cupula organs
are described by Fedele ( I 923a) and Millar (1953a) in Ciona inteatinaliv
as dome-shaped evagiriations arising from the mantle wall just inside
the atrial siphon (Fig. 26c). The dome consists of several ordinary sense
cells surrounded by supporting cells and the whole thing covered by test
material which is drawn out at the apex into a long process or flag.
This is the only part of the inner mantle wall where the power of test
secretion has been retained. Similar structures are known from pelagic
tunicates (Fedele, 1923c ; Bonc, 1959) but their function remains
obscure. Thc mantle cavity is ooncerncd with two principal types (Jf
response. It must respond to the presenc-e of faecw so as to eject them
through the atrial siphoii : thin is a simple rctflex action which hardly
requires such specialized structures as the cwpuh organs. The mantle