prcpartitions of Molguli suggvst that the concretion has a connective
framework in which tlir uric, acid grmules are embedded, and this
frumcwork is likely to I J ~
t i I)olystic,cIiurid(L. Although the evidence
available is limited thcrc is i i suggt4on throughout that the composition of rend cwicretioiis may not rcnlirin sttible and hence that they
may be engiiged in some active metabolic process. One such function
suggestcd by Nolfi is that they provide :L stable purine source for nuclei0
acid synthesis. However, this would involve in wivo synthesis of hypoxanthine from uric acid i~nd as Nolfi points out there is no evidence to
suggest that this is possible.
In summwy, ttscidians appear to I)c wliolly ammonotelic in their
protein metiibolism hiit are iiricotelia in rcaspect of niicleic acid metabolism iind in this renpecet difFer from rriost other aquatic invertebrates
which arc wholly tmmonotclio. Ttic stored uric acid i s derived hy
degradiitioii from piirinm arid not k ) . v do nowo synthesis and the abscnce
of urioolytic ciizyrncs prwenls further clcgracl;ition to allantoin or urea.
The functional significancc of uric acid storagc. remains obscure but it is
of such g c w d ocriirrenc*e in uscidians that further research is highly
desirable.
XI. THE NERVOUS SYSTEM
A clctttilctl review of the physiology of the nervous system in the
Tunicatit has rocently been published (Sullock and Horridge, 1966) crnd
little new intbrmat1ion has appearcd shoe that time. In the present
review an awount is provided of our prcsent knowledge of structure
and function in the ascidian nervous system with emphasis on those
features which are of special interest or significance in the physiology
of the group.
A. Strtccture of the nwvou,Y sydem
Ascidian nerves do not show up well with normal histological
techniques scich as silver impregnation or m14hylene blue staining and
in corisequence of this and the fineness of many of tho fihrcn therc: i x
still some uncwtainty about the details of tlic peripheral Hyntom. ‘I’tic
best accounts of the anatomy of the system are those of Hilton (1913)
who described the central ganglion of Ascidia nigra, Fedele (1923a,
1923b, 1927, 1937a) who described the peripheral nervous system in
Ciona intedinalis and Millar (1953a) who provides a general account of
nervous organization in Ciona inteetinalis. Other review articles are to
be found in Recligcr and Hartmeyer (1893-1911), Huus (1937), Brim
(1948) and Jhilloc~k and Horridge (1965). I n addition Markman (1958)
118s reported on a methylene b h and phase contrast ntudy of young
framework in which tlir uric, acid grmules are embedded, and this
frumcwork is likely to I J ~
t i I)olystic,cIiurid(L. Although the evidence
available is limited thcrc is i i suggt4on throughout that the composition of rend cwicretioiis may not rcnlirin sttible and hence that they
may be engiiged in some active metabolic process. One such function
suggestcd by Nolfi is that they provide :L stable purine source for nuclei0
acid synthesis. However, this would involve in wivo synthesis of hypoxanthine from uric acid i~nd as Nolfi points out there is no evidence to
suggest that this is possible.
In summwy, ttscidians appear to I)c wliolly ammonotelic in their
protein metiibolism hiit are iiricotelia in rcaspect of niicleic acid metabolism iind in this renpecet difFer from rriost other aquatic invertebrates
which arc wholly tmmonotclio. Ttic stored uric acid i s derived hy
degradiitioii from piirinm arid not k ) . v do nowo synthesis and the abscnce
of urioolytic ciizyrncs prwenls further clcgracl;ition to allantoin or urea.
The functional significancc of uric acid storagc. remains obscure but it is
of such g c w d ocriirrenc*e in uscidians that further research is highly
desirable.
XI. THE NERVOUS SYSTEM
A clctttilctl review of the physiology of the nervous system in the
Tunicatit has rocently been published (Sullock and Horridge, 1966) crnd
little new intbrmat1ion has appearcd shoe that time. In the present
review an awount is provided of our prcsent knowledge of structure
and function in the ascidian nervous system with emphasis on those
features which are of special interest or significance in the physiology
of the group.
A. Strtccture of the nwvou,Y sydem
Ascidian nerves do not show up well with normal histological
techniques scich as silver impregnation or m14hylene blue staining and
in corisequence of this and the fineness of many of tho fihrcn therc: i x
still some uncwtainty about the details of tlic peripheral Hyntom. ‘I’tic
best accounts of the anatomy of the system are those of Hilton (1913)
who described the central ganglion of Ascidia nigra, Fedele (1923a,
1923b, 1927, 1937a) who described the peripheral nervous system in
Ciona intedinalis and Millar (1953a) who provides a general account of
nervous organization in Ciona inteetinalis. Other review articles are to
be found in Recligcr and Hartmeyer (1893-1911), Huus (1937), Brim
(1948) and Jhilloc~k and Horridge (1965). I n addition Markman (1958)
118s reported on a methylene b h and phase contrast ntudy of young