TI1 E PHYXIOLO(IY OF ASClDIANH
31
considers to be specializcd for drawing the food cord from the stomach
into the intestine where it is l~assctf backwcwd by general ciliation and
folded back and forth across the prominent typhlosole (Morton, 1960).
The folding of the mucus cord in the stomach suggests that the mucus
envelope remains intact and its viscosity is not lowered as reported by
Yonge (1935) and Morton (1!)60). My own observations suggest that
any change in viscosity must occur at the junction of stomach and
intestine, and is of short duration and that the ring of ciliated cells may
have more importance in assisting the passage of a semi-fluid material
rather than in pulling the cord. The difference in function is small,
but its significance may be important mid is returned to later.
B. Histology of the alimentary canal
Most studies on the histology of the alimentary cans1 have been
based on Ciona intestinalis (Roulc, 1884 ; Yonge, 1925 ; Van Weel, 1940 ;
Millar, 19538,; Orsi, 1969; Thomas, 1970a,b) and the more complex
condition found in stolidobrarichs appears only to have been examined
by Fouque (1952, 1954, l959), 1)egaiI and Levi (1964), Orsi (1968) and
Croxall (1971).
1. The oesoph2ngua
Both Roulr and Yonge reported the existence of two types of cell in
the oesophagus, ciliated cells and mucus secreting cells. Yonge states
that the dorsal groove is composed of tall ciliated cells, while the ventral
groove ix composed of mucus secreting gland cells. In between the
grooves on the lateral walls of the oesophagus he found both ciliated
cells and mucux secreting cells. Millar also reports on the existence of
two types of cell in the oesophagus, mucus secreting ciliated cells in both
dorsal ltnd ventral grooves and tall ciliated cells in the remainder of the
oesophageltl wall. Foucpe, Orsi, Thomas and Croxall agree that there
is only a single cell-type, the ciliary-mucus cell in which the cilia are
confined marginally at the apex of the cell leaving room centrally for
the release of mucus.
It is not clear why there should be such a difference of interpretation
between different workers using the same species, but Thomas suggeuts
that the cells described by Millar and others as non-secretory may
merely be in lt transitional phase after discharging their secretion.
This seems unlikely in view of the distinct localization of cell types
reported by Mijlar. According to Thomaa (19708) the mucus, which i8
produced as granules from dilated cisternlte of the Golgi-body accumulates at the apex of the cell without any limiting membrane and i H
finally discharged by rupture of the apical plasma of the ccll. Orsi,
31
considers to be specializcd for drawing the food cord from the stomach
into the intestine where it is l~assctf backwcwd by general ciliation and
folded back and forth across the prominent typhlosole (Morton, 1960).
The folding of the mucus cord in the stomach suggests that the mucus
envelope remains intact and its viscosity is not lowered as reported by
Yonge (1935) and Morton (1!)60). My own observations suggest that
any change in viscosity must occur at the junction of stomach and
intestine, and is of short duration and that the ring of ciliated cells may
have more importance in assisting the passage of a semi-fluid material
rather than in pulling the cord. The difference in function is small,
but its significance may be important mid is returned to later.
B. Histology of the alimentary canal
Most studies on the histology of the alimentary cans1 have been
based on Ciona intestinalis (Roulc, 1884 ; Yonge, 1925 ; Van Weel, 1940 ;
Millar, 19538,; Orsi, 1969; Thomas, 1970a,b) and the more complex
condition found in stolidobrarichs appears only to have been examined
by Fouque (1952, 1954, l959), 1)egaiI and Levi (1964), Orsi (1968) and
Croxall (1971).
1. The oesoph2ngua
Both Roulr and Yonge reported the existence of two types of cell in
the oesophagus, ciliated cells and mucus secreting cells. Yonge states
that the dorsal groove is composed of tall ciliated cells, while the ventral
groove ix composed of mucus secreting gland cells. In between the
grooves on the lateral walls of the oesophagus he found both ciliated
cells and mucux secreting cells. Millar also reports on the existence of
two types of cell in the oesophagus, mucus secreting ciliated cells in both
dorsal ltnd ventral grooves and tall ciliated cells in the remainder of the
oesophageltl wall. Foucpe, Orsi, Thomas and Croxall agree that there
is only a single cell-type, the ciliary-mucus cell in which the cilia are
confined marginally at the apex of the cell leaving room centrally for
the release of mucus.
It is not clear why there should be such a difference of interpretation
between different workers using the same species, but Thomas suggeuts
that the cells described by Millar and others as non-secretory may
merely be in lt transitional phase after discharging their secretion.
This seems unlikely in view of the distinct localization of cell types
reported by Mijlar. According to Thomaa (19708) the mucus, which i8
produced as granules from dilated cisternlte of the Golgi-body accumulates at the apex of the cell without any limiting membrane and i H
finally discharged by rupture of the apical plasma of the ccll. Orsi,