(1969) using a catmula in the braiic*hial sac of Ascidia nigra found a
pressure of only 0.3 mm.
In additioii to the normal ciliary induced flow of water through the
branchial sac, ascidians also ex hibit regular contractions of the mantle
musculature which result in the discharge of about two-thirds of the
volume of water from both bratichid and atrial cavities. On relaxation
of the animal a fresh supply of water is drawn into these two cavities.
Spontaneous squirting of this sort has been studied in Ascidia nigra by
Hecht (1918a), in Styela clava Herdman by Yamaguchi (1931) and in
Phallusia mammillata by Hoyle (1963), and the subject has been
reviewed by Hoyle (loc. cit.) atid Ssrgensen (1966). In all these species
the frequency of Contraction is about one in every 6 to 8 min and
Yamaguchi and Hoyle are in agreement that in the absence of food
the rate increases to about once in every 2 min. However, Goodbody
and Trueman (1969) in a comparison of two species found that Aecidia
nigra exhibited a frequency of contractions of about once every
1.5 min, while A. interrupta Holler contracted about once in every
7.5 min. In contrast they showed that the pressure pulse induced by
contraction in A. nigra was about 2 cm of water as opposed to a pressure
of 6 cm of water in a similarly sized A. interrupta. Taking a human
analogy this may be likened to frequent small “ coughs ” by A. nigra
and infrequent large “ coughs ” by A. interruptu.
The functional significance of spontaneous squirting is still a matter
for debate. Hoyle (1953) considered that it is primarily associated with
food intake and is in this respect more important than ciliary activity.
He calculated that renewal of the water in the branchial sac by ciliary
activity amounted to about 1 rnl/min while squirting accounted for a
renewal of about 1.5 ml/min. The fact that spontaneous squirting
increases in frequency in the absence of food lcnt further support to
Hoyle’s argument. However, a~ pointed out by Jergensen ( I 955, 1966)
and Carlisle ( 1 966), Hoyle’s calvulations of renewal by ciliary activity
may have been erroneous. Jrargensen also points out that in Ciona
intestinalis at any rate renewal of water by squirting must be leHs than
90 ml/h, while renewal by ciliary activity is of the order of 3000 ml/h
or at least thirty times as great. Furthermore the water expelled in
squirting will probably remove as much particulate matter a8 is drawn
in in the subsequent inhalation (Jergen~en 1952, 1966). Jergenwn
(1966) has suggested that one function of squirting might be to renew
the water adjacent to the exterior of the siphons and thereby prevent
stagnation or any tendency to ro-cycle water between the atrial and
branchial siphons. While this effect may result from squirting activity
it is nnlikelg to be its primary functional role. The nervous control of
A.N.B.- I ?
2
pressure of only 0.3 mm.
In additioii to the normal ciliary induced flow of water through the
branchial sac, ascidians also ex hibit regular contractions of the mantle
musculature which result in the discharge of about two-thirds of the
volume of water from both bratichid and atrial cavities. On relaxation
of the animal a fresh supply of water is drawn into these two cavities.
Spontaneous squirting of this sort has been studied in Ascidia nigra by
Hecht (1918a), in Styela clava Herdman by Yamaguchi (1931) and in
Phallusia mammillata by Hoyle (1963), and the subject has been
reviewed by Hoyle (loc. cit.) atid Ssrgensen (1966). In all these species
the frequency of Contraction is about one in every 6 to 8 min and
Yamaguchi and Hoyle are in agreement that in the absence of food
the rate increases to about once in every 2 min. However, Goodbody
and Trueman (1969) in a comparison of two species found that Aecidia
nigra exhibited a frequency of contractions of about once every
1.5 min, while A. interrupta Holler contracted about once in every
7.5 min. In contrast they showed that the pressure pulse induced by
contraction in A. nigra was about 2 cm of water as opposed to a pressure
of 6 cm of water in a similarly sized A. interrupta. Taking a human
analogy this may be likened to frequent small “ coughs ” by A. nigra
and infrequent large “ coughs ” by A. interruptu.
The functional significance of spontaneous squirting is still a matter
for debate. Hoyle (1953) considered that it is primarily associated with
food intake and is in this respect more important than ciliary activity.
He calculated that renewal of the water in the branchial sac by ciliary
activity amounted to about 1 rnl/min while squirting accounted for a
renewal of about 1.5 ml/min. The fact that spontaneous squirting
increases in frequency in the absence of food lcnt further support to
Hoyle’s argument. However, a~ pointed out by Jergensen ( I 955, 1966)
and Carlisle ( 1 966), Hoyle’s calvulations of renewal by ciliary activity
may have been erroneous. Jrargensen also points out that in Ciona
intestinalis at any rate renewal of water by squirting must be leHs than
90 ml/h, while renewal by ciliary activity is of the order of 3000 ml/h
or at least thirty times as great. Furthermore the water expelled in
squirting will probably remove as much particulate matter a8 is drawn
in in the subsequent inhalation (Jergen~en 1952, 1966). Jergenwn
(1966) has suggested that one function of squirting might be to renew
the water adjacent to the exterior of the siphons and thereby prevent
stagnation or any tendency to ro-cycle water between the atrial and
branchial siphons. While this effect may result from squirting activity
it is nnlikelg to be its primary functional role. The nervous control of
A.N.B.- I ?
2