THE BIOLOGY OF ASCIDIANS
13
concluded that species of the primitive families had a longer breeding
season than those of more highly evolved families, but to generalize
from these observations would require a closer examination, bearing in
mind also the variation in season due to the location of species within
their total ranges.
Although water temperature largely controls breeding, the termination of the season does not appear to be closely related to a particular critical temperature. Several species in the Plymouth area cease
breeding while the water is still warm and food supply ample for adult
needs (Berrill, 1935b), and Dybern (1965) concluded that Ciona intestinalis stops spawning in autumn because of changes in the gonads
brought about by falling temperature rather than by a critical
temperature.
There is some evidence, however, that gametes are not released until
a certain temperature is reached (Huus, 1941) and that this is the temperature below which larval development is abnormal or impossible
(Knaben, 1952).
B. Spawning
Spawning in oviparous forms appears generally to take place at a
particular time of day and the resulting synchronization throughout a
population will increase the chances of fertilization. Ciona intestinalis
and Molgula manhattensis (De Kay) release eggs and sperm one to one
and a half hours before sunrise (Castle, 1896; Conklin, 1905; Berrill,
1947a) and Corella parallelogramma (Miiller) (Huus, 1939), and Styela
partita (Stimpson) do so in the late afternoon (Castle, 1896; Conklin,
1905; Rose, 1939). Hirai and Tsubata (1956) found that Halocynthia
roretzi (Drasche) kept in the laboratory for a few days repeatedly
spawned in the late morning.
The mechanism controlling synchronous release of gametes in
Corella parallelogramma depends on illumination following a period of
darkness (Huus, 1939). Huus (1941) later suggested that a hormone may
be involved. In Ciona intestinalis and Molgula manhattensis the gametes
are shed approximately 4 and 24 minutes respectively after the animals
are exposed to light, and the most effective light is of a wave-length
500-700 mp (Whittingham, 1967). Lambert and Brandt (1967) also
studied the effect of light on the spawning of Ciona intestinalis, and
after comparing the action spectrum for light-induced spawning with
the absorption spectrum of cytochrome c, concluded that this or some
other haemoprotein may be the receptor material.
Although somewhat beyond the scope of the present review it is
worth noting that many attempts have been made to discover whether
13
concluded that species of the primitive families had a longer breeding
season than those of more highly evolved families, but to generalize
from these observations would require a closer examination, bearing in
mind also the variation in season due to the location of species within
their total ranges.
Although water temperature largely controls breeding, the termination of the season does not appear to be closely related to a particular critical temperature. Several species in the Plymouth area cease
breeding while the water is still warm and food supply ample for adult
needs (Berrill, 1935b), and Dybern (1965) concluded that Ciona intestinalis stops spawning in autumn because of changes in the gonads
brought about by falling temperature rather than by a critical
temperature.
There is some evidence, however, that gametes are not released until
a certain temperature is reached (Huus, 1941) and that this is the temperature below which larval development is abnormal or impossible
(Knaben, 1952).
B. Spawning
Spawning in oviparous forms appears generally to take place at a
particular time of day and the resulting synchronization throughout a
population will increase the chances of fertilization. Ciona intestinalis
and Molgula manhattensis (De Kay) release eggs and sperm one to one
and a half hours before sunrise (Castle, 1896; Conklin, 1905; Berrill,
1947a) and Corella parallelogramma (Miiller) (Huus, 1939), and Styela
partita (Stimpson) do so in the late afternoon (Castle, 1896; Conklin,
1905; Rose, 1939). Hirai and Tsubata (1956) found that Halocynthia
roretzi (Drasche) kept in the laboratory for a few days repeatedly
spawned in the late morning.
The mechanism controlling synchronous release of gametes in
Corella parallelogramma depends on illumination following a period of
darkness (Huus, 1939). Huus (1941) later suggested that a hormone may
be involved. In Ciona intestinalis and Molgula manhattensis the gametes
are shed approximately 4 and 24 minutes respectively after the animals
are exposed to light, and the most effective light is of a wave-length
500-700 mp (Whittingham, 1967). Lambert and Brandt (1967) also
studied the effect of light on the spawning of Ciona intestinalis, and
after comparing the action spectrum for light-induced spawning with
the absorption spectrum of cytochrome c, concluded that this or some
other haemoprotein may be the receptor material.
Although somewhat beyond the scope of the present review it is
worth noting that many attempts have been made to discover whether