THE PHYSIOLO(IY O W ASCIDIANS
3
morphology. Indeed some of the most striking advances in our understanding of ascidian function have been made possible only through
recent work on the fine structure of such features as the test, the endostyle, the blood and the neural gland.
Because of their abundance and accessibility much of the work
which has been carried out on ascidian physiology has been on Ciona
intestinalis, Phallwia mammillata (Cuvier) or Ascidia nigra. The
first two are frequently referred to in the text simply as Ciona and
PWlusia. Ascidia nigra is a warm water species which strictly speaking
belongs to the sub-genus Phallusia and is frequently referred to in the
literature as Phallusia nigra, Phalluda atra or Aecidia atra ; the name
Ascidia nigra is now more widely accepted and is used throughout this
text. The use of biological nomenclature by physiologists leaves much
to be desired, and those working with ascidians are no exception.
Throughout the text of this review I have endeavoured to use the correct
nomenclature and have, in a few cases, altered the names as used by
original authors in their papers so as to make cross reference possible.
A wide Relection of taxonomic literature has been used in order to
check names, but in general the nomenclature of most of the animals
referred to in this text is to be found in either Van Name (1946),
Berrill (1950), Tokioka (1963) or Tokioka (1967).
For ease of reference the principal structures discussed in the text
are illustrated in Figs 1 and 2.
11. THE ASCIDIAN TEST
The test is an outer protective covering which completely surrounds
the individual zooid in solitary ascidians or forms a common groundwork in which the zooids are embedded in colonial species. It is soft
and flexible and varies in consistency from gelatinous to fibrous. In the
colonial aplousobranchs it is gelatinous, in the phlebobranchs and
particularly the Ascidiidae it is thick and slightly cartilaginous while
in some solitary stolidobranchs it is tough and almost leathery in
consistency. In many solitary forms there are blood vessels ramifying
throughout the test ; these arise from two test vessels one at either end
of the heart which cross the mantle and form vessels lined by a sin&
layer of epithelium (Das, 1936; Endean, 1966a). They form a network
of vessels with lateral branches ending in terminal bulbs particularly
toward the periphery (Fig. 3). Tn some colonial ascidians similar
stolonic vessels arising as epithelial outpushings penetrate info the test
substance. Blood cells, particularly morula cells, and in Halocynthia
aurantium ( Pallas) dispersed vesicular cells (Smith, 1970a), are found
throughout the test substance and apparently wander in there through
3
morphology. Indeed some of the most striking advances in our understanding of ascidian function have been made possible only through
recent work on the fine structure of such features as the test, the endostyle, the blood and the neural gland.
Because of their abundance and accessibility much of the work
which has been carried out on ascidian physiology has been on Ciona
intestinalis, Phallwia mammillata (Cuvier) or Ascidia nigra. The
first two are frequently referred to in the text simply as Ciona and
PWlusia. Ascidia nigra is a warm water species which strictly speaking
belongs to the sub-genus Phallusia and is frequently referred to in the
literature as Phallusia nigra, Phalluda atra or Aecidia atra ; the name
Ascidia nigra is now more widely accepted and is used throughout this
text. The use of biological nomenclature by physiologists leaves much
to be desired, and those working with ascidians are no exception.
Throughout the text of this review I have endeavoured to use the correct
nomenclature and have, in a few cases, altered the names as used by
original authors in their papers so as to make cross reference possible.
A wide Relection of taxonomic literature has been used in order to
check names, but in general the nomenclature of most of the animals
referred to in this text is to be found in either Van Name (1946),
Berrill (1950), Tokioka (1963) or Tokioka (1967).
For ease of reference the principal structures discussed in the text
are illustrated in Figs 1 and 2.
11. THE ASCIDIAN TEST
The test is an outer protective covering which completely surrounds
the individual zooid in solitary ascidians or forms a common groundwork in which the zooids are embedded in colonial species. It is soft
and flexible and varies in consistency from gelatinous to fibrous. In the
colonial aplousobranchs it is gelatinous, in the phlebobranchs and
particularly the Ascidiidae it is thick and slightly cartilaginous while
in some solitary stolidobranchs it is tough and almost leathery in
consistency. In many solitary forms there are blood vessels ramifying
throughout the test ; these arise from two test vessels one at either end
of the heart which cross the mantle and form vessels lined by a sin&
layer of epithelium (Das, 1936; Endean, 1966a). They form a network
of vessels with lateral branches ending in terminal bulbs particularly
toward the periphery (Fig. 3). Tn some colonial ascidians similar
stolonic vessels arising as epithelial outpushings penetrate info the test
substance. Blood cells, particularly morula cells, and in Halocynthia
aurantium ( Pallas) dispersed vesicular cells (Smith, 1970a), are found
throughout the test substance and apparently wander in there through