exterior. 111 t 1w Molgulidae tlwrc. is in iddition a large vesicle adjacent
to the heart which miitsins single (’oiicretion, partly composed of uric
acid, and in t h e Ascidiidtie t Iicrc ;ire 1 q e numbers of small concretions
usually hiit not always wniposed of uric acid or urates. These
vesicles are often refiwed to ss rcrial vesicles but as they can in
no way be compared to s kidney and are derived from the epicardium
which is a coelomic structure (Bcrrill, 1965) they are better referred to
as eoelomic vesicles. In Pyuridne and Styelidae vesicular evaginations
of the inantk wall, termed etidocwps, hang into the mantle cavity and
accumulate concretions or nephrocytes. In some Styelidae and Pyuridae
large deposits of uric acid may also acoumulate beneath the endostyle
and in other tissues. For a fuller description of these structures and
their contents we Aa6ma (1937), ])as (L948a), Goodbody (1954, 1965).
The existence of solid concretions of purines or uric acid led many
earlier worlccrs to conclude that ascidians were wholly uricotelic in their
nitrogen metabolism and Burian (L924) even went so far as to suggest
that they resembled snails, insects, reptiles iknd birds in this respect.
Most aquatic nnimids take tidvsritagc of t h e water to get rid of their
nitrogenous wastes as soluble ammonia anti it would be surprising if
asciditins did not do the same. Goodbody (1957) has shown that in
three species, Cioiia intestinalis, Ascidiella aspersa and Molgula manhattcnsis, ammonis is excreted in sufficient quantities t o suggeat that
their protein metabolism is essentially ammonotelic, and Sabbadin and
Tondonati (1 967) havc confirmed on a qualitative basis that ammonia
is also excreted hy Botryllus schlosseri (Pallas) and Botryllw leachi
(Savigny). ‘I’liese four species represent different types of ascidiim in
terms of uric acid or purine storage. Ciona intestinalis has an open
eoelom (epiciwdium) and no conmetions and according to Lambert,
quoted by Nolfi (1970), uric. arid has not been demonstrated in its
tissues : dscidiella aspersa has numerous coelomic vesicles but the
concretions ttre primarily formed of calcite (Goodbody, 1966) ; Botryllua
echlosseri and H. leachi have no visible coelom or vesicles but have a
very large quuittity of ncyhrocytcs, the concretions in which are almost
solely formed of uric wid (‘l’ondon:Lti slid SiLbbadin, 1960 ; Sabbadin
and Tondonati, 1967). MoZquZa rrzarrhattansis ha8 a single coelomic
vesicle c*ontaining s large concrct ion which i H composed of about 48%
uric acid (Goodbody, 1!)65; Nolfi, 1970) h u t may vary from 3‘g to
75% (Nolfi, loc. cit.).
The cvidenve favours the conclusion that ammonia in the principal
end-product o f nitrogen metabolism but that most, if not all, ascidians
aecumulute uric acid and possibly other purines such as xanthine,
guanine and adenine. The significance of such accumulations is lexx
to the heart which miitsins single (’oiicretion, partly composed of uric
acid, and in t h e Ascidiidtie t Iicrc ;ire 1 q e numbers of small concretions
usually hiit not always wniposed of uric acid or urates. These
vesicles are often refiwed to ss rcrial vesicles but as they can in
no way be compared to s kidney and are derived from the epicardium
which is a coelomic structure (Bcrrill, 1965) they are better referred to
as eoelomic vesicles. In Pyuridne and Styelidae vesicular evaginations
of the inantk wall, termed etidocwps, hang into the mantle cavity and
accumulate concretions or nephrocytes. In some Styelidae and Pyuridae
large deposits of uric acid may also acoumulate beneath the endostyle
and in other tissues. For a fuller description of these structures and
their contents we Aa6ma (1937), ])as (L948a), Goodbody (1954, 1965).
The existence of solid concretions of purines or uric acid led many
earlier worlccrs to conclude that ascidians were wholly uricotelic in their
nitrogen metabolism and Burian (L924) even went so far as to suggest
that they resembled snails, insects, reptiles iknd birds in this respect.
Most aquatic nnimids take tidvsritagc of t h e water to get rid of their
nitrogenous wastes as soluble ammonia anti it would be surprising if
asciditins did not do the same. Goodbody (1957) has shown that in
three species, Cioiia intestinalis, Ascidiella aspersa and Molgula manhattcnsis, ammonis is excreted in sufficient quantities t o suggeat that
their protein metabolism is essentially ammonotelic, and Sabbadin and
Tondonati (1 967) havc confirmed on a qualitative basis that ammonia
is also excreted hy Botryllus schlosseri (Pallas) and Botryllw leachi
(Savigny). ‘I’liese four species represent different types of ascidiim in
terms of uric acid or purine storage. Ciona intestinalis has an open
eoelom (epiciwdium) and no conmetions and according to Lambert,
quoted by Nolfi (1970), uric. arid has not been demonstrated in its
tissues : dscidiella aspersa has numerous coelomic vesicles but the
concretions ttre primarily formed of calcite (Goodbody, 1966) ; Botryllua
echlosseri and H. leachi have no visible coelom or vesicles but have a
very large quuittity of ncyhrocytcs, the concretions in which are almost
solely formed of uric wid (‘l’ondon:Lti slid SiLbbadin, 1960 ; Sabbadin
and Tondonati, 1967). MoZquZa rrzarrhattansis ha8 a single coelomic
vesicle c*ontaining s large concrct ion which i H composed of about 48%
uric acid (Goodbody, 1!)65; Nolfi, 1970) h u t may vary from 3‘g to
75% (Nolfi, loc. cit.).
The cvidenve favours the conclusion that ammonia in the principal
end-product o f nitrogen metabolism but that most, if not all, ascidians
aecumulute uric acid and possibly other purines such as xanthine,
guanine and adenine. The significance of such accumulations is lexx