2
IVAN QOODBODY
1. I NTRODUCTION
The liternture on ascidiims is extensive but no comprehensive
review of their physiolo&y seem ever to have been attempted. Following Kowalewsky’s (1867) discovery of their true systematic position
muoh of the early research on ascidians was directed towards elucidation
of their relationship with the chordates and the first serious attempt to
investigate their physiology seems to be the work of S. Hecht (191 6,
1918a, b, c, d, 1926) on Ascidia nigra (Savigny) and Ciona intestinalis
(Linnaeus). Subsequent workers concentrated on specific aspects of
physiology in the group often with emphasis on those functional aspects
which are unusual or which particularly illuminate problems of chordate
physiology. This applies especially to the universal occurrence of heart
beat reversal in all Tunicata and the existence of reducing compounds
in the blood often containing vanadium, both of which have been the
subject of much study. A t the same time, because of the simplicity of
their organization, they provide a useful material for certain types of
research, particularly developmental physiology, heart function and
the possible endocrinological role of the neural gland. With the exception of the nervous syRtem (Bullock and Horridge, 1965) there have
been few recent attempts to review any aspects of the literature on
ascidian physiology and hence it is often necessary to refer back quite
far for source material.
It is difficult for a single person to encompass in detail all of the
many facets of physiology contained in the literature on ascidians and
I have been deliberately selective in the topics chosen for discussion.
The literaturc. on ascidian en1 bryology has been reviewed recently by
Reverberi (1961, 1971) and I liave made no attempt to discum developmental physiology. Nor have I discussed larval physiology, which
presents special problems associated with a free swimming mode of life,
and would be better included in a separate review of larval biology au
a whole. Finally, I have not attempted to include a discussion of any
special problems of the pelagic Tunicata although, where appropriate,
reference is made to them.
I n preparing this review 1 have been guided in the selection of
material and the mode of presentation by an attempt to consider
problems in the light of their relevance to ascidian biology and not
their specific relevance to comparative physiology. In the process some
papers and some problems have been omitted or passed over rather
briefly. Structure and function are inseparable aspects of biology and
in order to elaborate many points in the animals’ physiology it has
been necessary to include some material which is essentially descriptive
IVAN QOODBODY
1. I NTRODUCTION
The liternture on ascidiims is extensive but no comprehensive
review of their physiolo&y seem ever to have been attempted. Following Kowalewsky’s (1867) discovery of their true systematic position
muoh of the early research on ascidians was directed towards elucidation
of their relationship with the chordates and the first serious attempt to
investigate their physiology seems to be the work of S. Hecht (191 6,
1918a, b, c, d, 1926) on Ascidia nigra (Savigny) and Ciona intestinalis
(Linnaeus). Subsequent workers concentrated on specific aspects of
physiology in the group often with emphasis on those functional aspects
which are unusual or which particularly illuminate problems of chordate
physiology. This applies especially to the universal occurrence of heart
beat reversal in all Tunicata and the existence of reducing compounds
in the blood often containing vanadium, both of which have been the
subject of much study. A t the same time, because of the simplicity of
their organization, they provide a useful material for certain types of
research, particularly developmental physiology, heart function and
the possible endocrinological role of the neural gland. With the exception of the nervous syRtem (Bullock and Horridge, 1965) there have
been few recent attempts to review any aspects of the literature on
ascidian physiology and hence it is often necessary to refer back quite
far for source material.
It is difficult for a single person to encompass in detail all of the
many facets of physiology contained in the literature on ascidians and
I have been deliberately selective in the topics chosen for discussion.
The literaturc. on ascidian en1 bryology has been reviewed recently by
Reverberi (1961, 1971) and I liave made no attempt to discum developmental physiology. Nor have I discussed larval physiology, which
presents special problems associated with a free swimming mode of life,
and would be better included in a separate review of larval biology au
a whole. Finally, I have not attempted to include a discussion of any
special problems of the pelagic Tunicata although, where appropriate,
reference is made to them.
I n preparing this review 1 have been guided in the selection of
material and the mode of presentation by an attempt to consider
problems in the light of their relevance to ascidian biology and not
their specific relevance to comparative physiology. In the process some
papers and some problems have been omitted or passed over rather
briefly. Structure and function are inseparable aspects of biology and
in order to elaborate many points in the animals’ physiology it has
been necessary to include some material which is essentially descriptive