uptake by A . nigra is very similar to that of other sessile animals
metabolizing at similar ten1 peratures (Table VII).
TABLE VII. o X U U E N UPTAKE (pL/H/CI D R Y WT) 1N h c i d i a COMPARED WITH
‘ r H R E I HIVALVES AT SIMl LAR l
Oxygen
7 lptake
‘I’ernp.
Atither
.
__
Aacidia nigren
28
1630
Goodbody and Young
(oxclridiirg twt woiglii)
(unpublished)
Ascidia nigra
(incliiditig twt, wcriglit)
48
806
Goodbody and Young
Cramoutreen uirginica (GIKL)
34.5
ti45 -1504 Galtsoff and Whipple
Mytiltis etttdix L.
25.3
ti86
Head (1962)
Brmhidontes tlemilu.uus Liiinurck
28.2
1059
Read (1962)
( 1930)
The low rate of gaseous exchange in ascidians makes the existence
of specialized respiratory organs unnecessary ; nevertheless, the primary
site of gaseous exchange is by no means certain. It is usually assumed
that the large surface area o f the branchial sac provides the major area
of respiratory exrhange but, whilc this is n reasonable assumption, it is
also likely that Ihe inner sirrfarr of the mantle wall may provide a
secondary site of exchange.
VIII. THE CIIWITLATORY SYSTEM
Thr ascidinn cirrulaLtory system consists of a tubular heart enclosed
in a pericardium and connecting at either end to a system of blood
vessels and chtinnels which ramify throughout the body and test. The
principal features of this system are illustrated in Fig. 2 (p. 5). At one
end of the heart,, the hypobranchial end, a large sinus is given off to run
under the endostyle and a Recond sinus crosses through the body wall to
supply the test. The subendostylar sinus supplies branches to the body
wall and to the branchial sac. From the branchial sac blood collects
into a dorsal brnnchial vessel which also receives blood from the body
and itself delivers blood to the alimentary canal. A series of blood
spaces and channelx circulate the blood around the viscera before
collecting again into a visceral vessel which rejoins the heart at the
visceral end where a second test sinus also joins. NOJE of the blood
apacex is a true blood vessel as an eiidothelial lining is lacking, but the
principal channels, such as the subendostylur sinus have a connective
metabolizing at similar ten1 peratures (Table VII).
TABLE VII. o X U U E N UPTAKE (pL/H/CI D R Y WT) 1N h c i d i a COMPARED WITH
‘ r H R E I HIVALVES AT SIMl LAR l
Oxygen
7 lptake
‘I’ernp.
Atither
.
__
Aacidia nigren
28
1630
Goodbody and Young
(oxclridiirg twt woiglii)
(unpublished)
Ascidia nigra
(incliiditig twt, wcriglit)
48
806
Goodbody and Young
Cramoutreen uirginica (GIKL)
34.5
ti45 -1504 Galtsoff and Whipple
Mytiltis etttdix L.
25.3
ti86
Head (1962)
Brmhidontes tlemilu.uus Liiinurck
28.2
1059
Read (1962)
( 1930)
The low rate of gaseous exchange in ascidians makes the existence
of specialized respiratory organs unnecessary ; nevertheless, the primary
site of gaseous exchange is by no means certain. It is usually assumed
that the large surface area o f the branchial sac provides the major area
of respiratory exrhange but, whilc this is n reasonable assumption, it is
also likely that Ihe inner sirrfarr of the mantle wall may provide a
secondary site of exchange.
VIII. THE CIIWITLATORY SYSTEM
Thr ascidinn cirrulaLtory system consists of a tubular heart enclosed
in a pericardium and connecting at either end to a system of blood
vessels and chtinnels which ramify throughout the body and test. The
principal features of this system are illustrated in Fig. 2 (p. 5). At one
end of the heart,, the hypobranchial end, a large sinus is given off to run
under the endostyle and a Recond sinus crosses through the body wall to
supply the test. The subendostylar sinus supplies branches to the body
wall and to the branchial sac. From the branchial sac blood collects
into a dorsal brnnchial vessel which also receives blood from the body
and itself delivers blood to the alimentary canal. A series of blood
spaces and channelx circulate the blood around the viscera before
collecting again into a visceral vessel which rejoins the heart at the
visceral end where a second test sinus also joins. NOJE of the blood
apacex is a true blood vessel as an eiidothelial lining is lacking, but the
principal channels, such as the subendostylur sinus have a connective