tc’rorn thesc- accounts of the gt&ri(> epithelium i t is possible to
identify the follo\king general cell types :
(i) Mucus secreting c d s . These only occur in conducting areas of the
stomach i.c. in the ventrnl fold of Ciona (Thomas, 1970b) and in the
ducts of the digestive glund in Pyuridac (Degail and Levi, 1964).
(ii) Vacuolar secwtor?/ cells, found on the crests of the ridges in Ciona
(Thomas, l970b) and in the wall of the diverticulum in Pyuridae
(l!ouque, 1959 ; Uegail aid Lcvi, I !Mia). In Ciona Thomas found that
the vacuoles cwntain curbohydi.iite-proteiti complexes, lipids, free amino
groups, t ryptophan, non-specific esterase and acid phosphataae activity.
Similar swretions hive been identified in 8tyela by C h i (1968) and in
Cowlla, dslerocarpa, (’uemidocarpa and Styela by Croxall (I971 ).
Thomas points out t hat the enzymes, I)articularly acid phosphatase, are
characteristic of cells engaged in intracellular digestion (see de Duve,
1963) and thtbt the f i n c h structure of the vacuole resembles that of a
lysosome. Thomas suggests that these cells may produce an unusual
secretion even though lysosomal enzymes do not normally have an
extmcellulnr role. It ie of interest to note, therefore, that these are the
aolls which Yorige ( 1925) considered to have an absorptive role in Ciona
and which Viin Wecl (1940) reported as taking up particulate iron
saccharato. Tlit~y are probably equivalent to Morton’s (1960) Type A
cells in 8alpa.
(iii) Busophilir* cells, found iii the walls of the ridges in Ciona and in
the wdls of the divcrtiw1;i in Pyuridw. 1)cgail and Levi ( I 964) believed
that those rc4s scwoled mucus, but in Ciona Thomas (1970b) reports
that t,hey produw iL sero-mucus secrt+on particwlarly rich in proteins
and he notw tliiit their fine strrrctmrc Iwemhles that of protein secreting
cells in ot hcr organisms. He conc.liic1t.s that thcsc are enzymc secreting
cells. ‘I’hey twt’ probably eqtrivitknt to Mortori’s ( I 960) ‘J’ypc B celln
described in Ralprc. Morton consitlered his Type B cells to be equivalent
to those found by Barrington (1!)36, 1937) in the intestine of the emmocmoete and in the digewtive diverticulum of Amphigxus (Branchiostm).
He further related these to the zymogen cells of the pancreas in higher
chordates and therefore concluded that the digestive diverticulum of
the tunicate should be regarded as the beginnings of a pancreas and
not of a liver.
3. The mid-intestine
The histology of the mid-intestine of Ciona has been described by a
number of authors including Yonge (1925), Van Wee1 (1940), Millar
( 1963a), Fouque ( I964), Thomas (19704 and Croxall (1 971 ), but there
i R a conspicuous lack of precise detail in these accountR. There appet~I
identify the follo\king general cell types :
(i) Mucus secreting c d s . These only occur in conducting areas of the
stomach i.c. in the ventrnl fold of Ciona (Thomas, 1970b) and in the
ducts of the digestive glund in Pyuridac (Degail and Levi, 1964).
(ii) Vacuolar secwtor?/ cells, found on the crests of the ridges in Ciona
(Thomas, l970b) and in the wall of the diverticulum in Pyuridae
(l!ouque, 1959 ; Uegail aid Lcvi, I !Mia). In Ciona Thomas found that
the vacuoles cwntain curbohydi.iite-proteiti complexes, lipids, free amino
groups, t ryptophan, non-specific esterase and acid phosphataae activity.
Similar swretions hive been identified in 8tyela by C h i (1968) and in
Cowlla, dslerocarpa, (’uemidocarpa and Styela by Croxall (I971 ).
Thomas points out t hat the enzymes, I)articularly acid phosphatase, are
characteristic of cells engaged in intracellular digestion (see de Duve,
1963) and thtbt the f i n c h structure of the vacuole resembles that of a
lysosome. Thomas suggests that these cells may produce an unusual
secretion even though lysosomal enzymes do not normally have an
extmcellulnr role. It ie of interest to note, therefore, that these are the
aolls which Yorige ( 1925) considered to have an absorptive role in Ciona
and which Viin Wecl (1940) reported as taking up particulate iron
saccharato. Tlit~y are probably equivalent to Morton’s (1960) Type A
cells in 8alpa.
(iii) Busophilir* cells, found iii the walls of the ridges in Ciona and in
the wdls of the divcrtiw1;i in Pyuridw. 1)cgail and Levi ( I 964) believed
that those rc4s scwoled mucus, but in Ciona Thomas (1970b) reports
that t,hey produw iL sero-mucus secrt+on particwlarly rich in proteins
and he notw tliiit their fine strrrctmrc Iwemhles that of protein secreting
cells in ot hcr organisms. He conc.liic1t.s that thcsc are enzymc secreting
cells. ‘I’hey twt’ probably eqtrivitknt to Mortori’s ( I 960) ‘J’ypc B celln
described in Ralprc. Morton consitlered his Type B cells to be equivalent
to those found by Barrington (1!)36, 1937) in the intestine of the emmocmoete and in the digewtive diverticulum of Amphigxus (Branchiostm).
He further related these to the zymogen cells of the pancreas in higher
chordates and therefore concluded that the digestive diverticulum of
the tunicate should be regarded as the beginnings of a pancreas and
not of a liver.
3. The mid-intestine
The histology of the mid-intestine of Ciona has been described by a
number of authors including Yonge (1925), Van Wee1 (1940), Millar
( 1963a), Fouque ( I964), Thomas (19704 and Croxall (1 971 ), but there
i R a conspicuous lack of precise detail in these accountR. There appet~I