reports that at Rosooff, the same spccies (Ciona intestinalis) has two
cycles in 24 hours.
There tire differing opitiions conc.erning the fate of the cells discharged into the lumcm of the gland. YBr& (1943), who believed that
the gland was primarily plwgocytic, insisfcd that the ciliary currents
in the canal were such as to create an outward movement down the
centre of the canal carrying material from the gland to the pharynx.
This is supported by Millar (1953a) who showed that cilia around the
periphery of the ciliated funnel draw water inwards. The currents only
make a shallow penetration before being directed out again by cilia of
the median border. These heat outward and drive water away from the
funnel and thus the water flow is such as to wash cells out of the funnel.
However, Georgcs (1 970, 1971 ) is equally emphatic that the ciliary
currents of the canal beat inward from pharynx to gland and considers
that the contents of the cells may diffuse into the blood stream and thus
permit the gland t,o function au an endocrine organ. She liken8 the
connective Rheath nrouiid the gland to the tunica propria of the insect
prothorecia gland and suggests that it may be intimately concerned
with the passage of material from gland to blood stream.
B. Origin of the neural fllnnd
Before bonsiderinp the function of the neural gland it is relevant to
examine its embryological origin and its relation to the nerve ganglion.
According .to Elwyn ( 1 937), who also reviews the older literature, the
anterior psition of the nrural tube after closure of the neuropore
divides longitudinally into two tubes. The right side immediately gives
rise to the 'sensory vesicle of thc larva while the tube on the left side
becomes the " neurohypophysis " and will later give rise to both neural
gland and derve ganglion. The " neurohypophysis " is at first blind at
both ends but the anterior end grows forward and eventually forces an
opening into the anterior portion of the pharynx. Elwyn shows micrographs of sbcfioncd material to demonstrate that the remltant duct of
the neural gland is entirely of " neurohypophysial " origin and neither
pharyngeal'mdoderrn nor stornodaeurn contribute any tissueN to tho
gland or duct. Furthermore the opening into the pharynx i N complete
before the stomodaeum has broken through to the pharynx. The norve
ganglion is formed by proliferation from the dorsal wall of the neurohypoyhyBis except in Stolidobranchiata where it pro1iferutt:s from the
ventral wall.
cycles in 24 hours.
There tire differing opitiions conc.erning the fate of the cells discharged into the lumcm of the gland. YBr& (1943), who believed that
the gland was primarily plwgocytic, insisfcd that the ciliary currents
in the canal were such as to create an outward movement down the
centre of the canal carrying material from the gland to the pharynx.
This is supported by Millar (1953a) who showed that cilia around the
periphery of the ciliated funnel draw water inwards. The currents only
make a shallow penetration before being directed out again by cilia of
the median border. These heat outward and drive water away from the
funnel and thus the water flow is such as to wash cells out of the funnel.
However, Georgcs (1 970, 1971 ) is equally emphatic that the ciliary
currents of the canal beat inward from pharynx to gland and considers
that the contents of the cells may diffuse into the blood stream and thus
permit the gland t,o function au an endocrine organ. She liken8 the
connective Rheath nrouiid the gland to the tunica propria of the insect
prothorecia gland and suggests that it may be intimately concerned
with the passage of material from gland to blood stream.
B. Origin of the neural fllnnd
Before bonsiderinp the function of the neural gland it is relevant to
examine its embryological origin and its relation to the nerve ganglion.
According .to Elwyn ( 1 937), who also reviews the older literature, the
anterior psition of the nrural tube after closure of the neuropore
divides longitudinally into two tubes. The right side immediately gives
rise to the 'sensory vesicle of thc larva while the tube on the left side
becomes the " neurohypophysis " and will later give rise to both neural
gland and derve ganglion. The " neurohypophysis " is at first blind at
both ends but the anterior end grows forward and eventually forces an
opening into the anterior portion of the pharynx. Elwyn shows micrographs of sbcfioncd material to demonstrate that the remltant duct of
the neural gland is entirely of " neurohypophysial " origin and neither
pharyngeal'mdoderrn nor stornodaeurn contribute any tissueN to tho
gland or duct. Furthermore the opening into the pharynx i N complete
before the stomodaeum has broken through to the pharynx. The norve
ganglion is formed by proliferation from the dorsal wall of the neurohypoyhyBis except in Stolidobranchiata where it pro1iferutt:s from the
ventral wall.