THE PHYSIOLOGY OF ASCIDIANS
67
his co-workers (1961b,c) consider that this is insufficient to permit such
a mechanism ; furthermore, labelled sulphate absorbed by Ciona is
retained in a completely dialysable form and cannot be protein bound.
Using labelled sodium sulphate, Bielig et aZ. (1961b,c) found that after
48 hours immersion the ratio of activity in sea water to plasma was
100 to 52 ; uptake of sulphate is temperature dependent and has a Ql0
of 1.8. The rate of uptake is enhanced by the addition of vanadate and
there is a shift in the ratio of sulphate in sea water and plasma resulting
in a higher plasma concentrahion. Ascidians are totally lacking in any
form of conventional excretory organ and in the light of the above it
seemx likely that sulphute regulittion is maintained by active transport
acroxs the X)rttriohiiLlel)ithcliiim (Bicdigcatal., 196Ib). It ix of interest that
the situiLtion ix ~ ) i ~ ~ i ~ l l ~ l ~ ! ( I
in tho rnc~)gloeo of the xcyphomt!duncm,
Aureliu avritri I,., w h r w xirniler lmgv rrvluc:tions of Hulphato have been
recordcd in thr: abnerict: of m y cxcrotory organ (Itobertson, 1949).
B. Blood cells
All ascidian blood cells arise from haemoblasts of mesenchymatous
origin located in the vicinity of connective tissue particularly around
the alimentary canal and branchial sac: (Cowden, 1968 ; Millar, 1953a ;
PBrAs, 1943, 1945). The haemoblasts are able to give rise to either
connective tissue cells or lymphocytes from which all other blood cell
types are derived.
Before attempting to discuss the functions of the blood it is necessary
to clarify the nature of the cells of which it is composed. This is made
difficult by confusion in description and terminology presented by
various authors. The first comprchensive description of the cc!llulltr
elements is probably that of Fulton (1920), but George's ( 1 !)39) review
provides a more accurate account from which to ham Ilttw xtudi(1~.
Since the publication of George’s revicw, tlenariptions of c~rcaitlian hlood
have been published by lt numher of workcrs including 1’6ri:x (1943),
Endcan ( 1 9rjrja, 1960), Millar (1953iL), Sthhhatlin ( I !)!it$ 1 W A ) , Frwrnuri
(1964), Overton ( I Sf%), Vallcc ( I %;?a), Smith ( I 970a). ‘I‘he torminology
used by these authors is not always thc same but from a study of thcir
papers and of the blood itself it is possible to identify eight types of cell
as described below.
(a) Lymphocyte. This is anundifferentiatedcell about 5 p in diameter
and resembling the mammalian lymphocyte. It has a large nucleus but
no nucleolus and apparently gives rise to all other blood cell types.
The lymphocyte also plays an important role in the development of
young buds during asexual reproduction of such species as Perophorn
67
his co-workers (1961b,c) consider that this is insufficient to permit such
a mechanism ; furthermore, labelled sulphate absorbed by Ciona is
retained in a completely dialysable form and cannot be protein bound.
Using labelled sodium sulphate, Bielig et aZ. (1961b,c) found that after
48 hours immersion the ratio of activity in sea water to plasma was
100 to 52 ; uptake of sulphate is temperature dependent and has a Ql0
of 1.8. The rate of uptake is enhanced by the addition of vanadate and
there is a shift in the ratio of sulphate in sea water and plasma resulting
in a higher plasma concentrahion. Ascidians are totally lacking in any
form of conventional excretory organ and in the light of the above it
seemx likely that sulphute regulittion is maintained by active transport
acroxs the X)rttriohiiLlel)ithcliiim (Bicdigcatal., 196Ib). It ix of interest that
the situiLtion ix ~ ) i ~ ~ i ~ l l ~ l ~ ! ( I
in tho rnc~)gloeo of the xcyphomt!duncm,
Aureliu avritri I,., w h r w xirniler lmgv rrvluc:tions of Hulphato have been
recordcd in thr: abnerict: of m y cxcrotory organ (Itobertson, 1949).
B. Blood cells
All ascidian blood cells arise from haemoblasts of mesenchymatous
origin located in the vicinity of connective tissue particularly around
the alimentary canal and branchial sac: (Cowden, 1968 ; Millar, 1953a ;
PBrAs, 1943, 1945). The haemoblasts are able to give rise to either
connective tissue cells or lymphocytes from which all other blood cell
types are derived.
Before attempting to discuss the functions of the blood it is necessary
to clarify the nature of the cells of which it is composed. This is made
difficult by confusion in description and terminology presented by
various authors. The first comprchensive description of the cc!llulltr
elements is probably that of Fulton (1920), but George's ( 1 !)39) review
provides a more accurate account from which to ham Ilttw xtudi(1~.
Since the publication of George’s revicw, tlenariptions of c~rcaitlian hlood
have been published by lt numher of workcrs including 1’6ri:x (1943),
Endcan ( 1 9rjrja, 1960), Millar (1953iL), Sthhhatlin ( I !)!it$ 1 W A ) , Frwrnuri
(1964), Overton ( I Sf%), Vallcc ( I %;?a), Smith ( I 970a). ‘I‘he torminology
used by these authors is not always thc same but from a study of thcir
papers and of the blood itself it is possible to identify eight types of cell
as described below.
(a) Lymphocyte. This is anundifferentiatedcell about 5 p in diameter
and resembling the mammalian lymphocyte. It has a large nucleus but
no nucleolus and apparently gives rise to all other blood cell types.
The lymphocyte also plays an important role in the development of
young buds during asexual reproduction of such species as Perophorn