I f t,Iiis int~crpretat~ioti is (v)iwc*t it riiay I c ~ d to an explanation of the
avid f i l l ~ d bliidder ( ~ 1 1 9 or tlwt vwi(+bs found in the test of some ascidians
(Webh. I !):)!I ; St,ii.vc.iictrL. I!)70). ‘I’li(~s(~ vesicles art- not, trot) oc4s lnit
arc nicivly iltiid fillotl c+ripwl(*x t i t i t 1 I C i i ~ l ~ ~ i
(I!Nil ) JIILH Hltowu how t ticy
mny fortit iiroiitid
If the- purposp of thc
acid in t h niorula c.cll is to liolil t,lic. c*liromogcn in a rcduced state
until it is i n H position to perform its fiiiiction of fibre production then,
when this fiiiiction is ft~lfilletl, it is ckarly desirable to remove the
acid and not to ptwnit it to diffusc through tht. test substance. This
could be frilfilled by ciioapsulating tjhe acid in the test vesicles and
subsequently discharging thrsc through the surface of the test.
( ~ i ~ i t i t ~ ( ~ g ~ . i ~ t i i t ~
iitorulrr. wII.
111. ‘I’HE BHANOHIAL SAC
Thc t)rtmcIiial s a c , or phsryiix. inlist be considered as serving the
dual roles of ti food co1Irtc:ti~ig upparutus and IL site of gaseous exchange
wit,h the wILt.er. L n it,* simplest, form, its forind in aplousobranchiate
twcidians, it, is (I sac-liko striwturc the lateral walls of which are pierced
by stiginatii. t?acti onc of which is fringed with cilia; these cilia are
responsible for driving the wLtei* crirrc*nt t,hrough the sac. Along the
ventral margin of the sac is iLii etidostjyle whose primary function is to
mcrete miiciis which is diroctccl ILR ti shcct passing across the walls of
tho sac: to the dorsel side w1itu.e it is folded into a mucus cord by the
dorsal LLrniriib.* The o r d cntrtitict: t,o tho Sit(> is guarded by a circle of
tentacles which tLct as ti coarse filtw for particles entering the sac in
tho wattor st,rciirn. In p1ilebobr;~tioliiate ascidians the inner wall of the
breiichial stic is complicated 1)y tlhc presence of internal longitudinai
bars borne on pedicel-like outgrowths frorii the wall of the sac. At the
junctions of int,enial longitudinal bars and transverse vessels small
ciliated papilltie extend inwards towards the cavity of the sac. Similar
interns1 longit,udinad bttrs, lacking papillae. occur in the stolidobrunchinte ttscidians but, in this groiip the whole wall of the branchial
sac is throwii into II series of folds thus greatly increasing the internal
surfacc. iirea: ’i’tiese ditrerences must) he asso(-iated with differences in
the feeding notivity of t2he animals coric.ernet1, but until recently little
nt,t,ention ha,s heen given to their functional significance. Nor doe8
anyone seein to have cwisidertid the functional significance of differences
which occur in the structrire of the dorsal lamina.
The feeding mechanism of ascidians has been fully described by
* The word mitrim i~ IIHWI t,hroiigh~~iit tho t w t iri w r y gorwal ltrrrnn t,r, tlanoriho thrt
eocrot.ioti from tho (wdwt~,vli-. ‘Yho r)rw:int* chtwlionl ticlt lirtv r,f‘ 1 ttfj wcrt:tit)Ii in iinrv,rt,ain
but it, corit,nin* lavgv I L I I I I ~ I I I I ~ ~
i i f ‘ ( t i i i o t l i r i i ~ t i v l prot.t3in in atltlitiori to rriilciis c l r r ~ t rnny ho
n rnr~co-l~ri~t~c*iri.
avid f i l l ~ d bliidder ( ~ 1 1 9 or tlwt vwi(+bs found in the test of some ascidians
(Webh. I !):)!I ; St,ii.vc.iictrL. I!)70). ‘I’li(~s(~ vesicles art- not, trot) oc4s lnit
arc nicivly iltiid fillotl c+ripwl(*x t i t i t 1 I C i i ~ l ~ ~ i
(I!Nil ) JIILH Hltowu how t ticy
mny fortit iiroiitid
If the- purposp of thc
acid in t h niorula c.cll is to liolil t,lic. c*liromogcn in a rcduced state
until it is i n H position to perform its fiiiiction of fibre production then,
when this fiiiiction is ft~lfilletl, it is ckarly desirable to remove the
acid and not to ptwnit it to diffusc through tht. test substance. This
could be frilfilled by ciioapsulating tjhe acid in the test vesicles and
subsequently discharging thrsc through the surface of the test.
( ~ i ~ i t i t ~ ( ~ g ~ . i ~ t i i t ~
iitorulrr. wII.
111. ‘I’HE BHANOHIAL SAC
Thc t)rtmcIiial s a c , or phsryiix. inlist be considered as serving the
dual roles of ti food co1Irtc:ti~ig upparutus and IL site of gaseous exchange
wit,h the wILt.er. L n it,* simplest, form, its forind in aplousobranchiate
twcidians, it, is (I sac-liko striwturc the lateral walls of which are pierced
by stiginatii. t?acti onc of which is fringed with cilia; these cilia are
responsible for driving the wLtei* crirrc*nt t,hrough the sac. Along the
ventral margin of the sac is iLii etidostjyle whose primary function is to
mcrete miiciis which is diroctccl ILR ti shcct passing across the walls of
tho sac: to the dorsel side w1itu.e it is folded into a mucus cord by the
dorsal LLrniriib.* The o r d cntrtitict: t,o tho Sit(> is guarded by a circle of
tentacles which tLct as ti coarse filtw for particles entering the sac in
tho wattor st,rciirn. In p1ilebobr;~tioliiate ascidians the inner wall of the
breiichial stic is complicated 1)y tlhc presence of internal longitudinai
bars borne on pedicel-like outgrowths frorii the wall of the sac. At the
junctions of int,enial longitudinal bars and transverse vessels small
ciliated papilltie extend inwards towards the cavity of the sac. Similar
interns1 longit,udinad bttrs, lacking papillae. occur in the stolidobrunchinte ttscidians but, in this groiip the whole wall of the branchial
sac is throwii into II series of folds thus greatly increasing the internal
surfacc. iirea: ’i’tiese ditrerences must) he asso(-iated with differences in
the feeding notivity of t2he animals coric.ernet1, but until recently little
nt,t,ention ha,s heen given to their functional significance. Nor doe8
anyone seein to have cwisidertid the functional significance of differences
which occur in the structrire of the dorsal lamina.
The feeding mechanism of ascidians has been fully described by
* The word mitrim i~ IIHWI t,hroiigh~~iit tho t w t iri w r y gorwal ltrrrnn t,r, tlanoriho thrt
eocrot.ioti from tho (wdwt~,vli-. ‘Yho r)rw:int* chtwlionl ticlt lirtv r,f‘ 1 ttfj wcrt:tit)Ii in iinrv,rt,ain
but it, corit,nin* lavgv I L I I I I ~ I I I I ~ ~
i i f ‘ ( t i i i o t l i r i i ~ t i v l prot.t3in in atltlitiori to rriilciis c l r r ~ t rnny ho
n rnr~co-l~ri~t~c*iri.