THJC PHYBIOLOOY OF ABCIDIANS
23
IV. THE I':NDOSTYLE
The endostyle f'ormn a shdlow groove extending along the whole
length of the ventrnl side of the braiichial sac. The morphology and
histology of this structure hax been reviewed by a number of authors
including Soldska (1931), Raimbault ( I 948), Barrington (1957),
Olsson (1963) and Orsi and Relini (I966a,b) and details of ultrastructure and histoohemistry of the various regions are given by Levi
and Yorte (1964), Godeiiux am1 Firket, (1966, I968), Ghiani et al.
( 1 965), Ghiani and Orsi ( 1 !Isti), Aros and Vir&gh (1 MI)), Godeclux (1 97 I )
and Thorpc PI aE. (1972).
'I'herr is roirsiderablc uniformity in t h structure of the endostyle in
different specivs aiid in gcneriil it is dividod into eight regions or zones
as illustrated in Fig. H. An idditional small group of cells between
zones 4 iintl 5 has becn drsrribed by Orsi m d Relini (1966a) and
Codeaux and Firket ( 1 968) wid another small group between zones 7
and 8 in the family Pyuridar by Orsi and Relini (1986a,b) and in
Ciona by 'l'hirbold (197 I ) .
Zone 1 at the base of the groove is unpaired and is composed of tall
cells arraiigcd on either side of' a groove marking the median plane of
the endostyle. Thrse cells con1 ain large, electron dense granules about
700 A in diameter and a number of microtubules and microfibrils.
A t the apex the cells bear l o ~ g flagella surrounded at their base by
numerous finger-like microvilli (Godeaux and Firket, 1968 ; Ghiani and
Orsi, 1966 ; AroH and Virligh, I969). Arcording to many authors these
cells produce i i secretion of mumis (Levi and Porte, 1964 ; Barrington,
1957; Ghiani and Orsi, 1966: T h o r p ~t al., 1!172), but Olsson (1963)
itlid Godeaux and Firkct ( I96H) 110th considrr that the granular contents of the cell are glycwgen and not mucus. The flagella appear to be
used to sprestl secretions from other zones throughout the enclostylar
groovc itnd to assist in wafting them out towardx tho walls of thc
hi*~nc~hi;il sac.
Zones 2 and 4 are composed of a nmall number of very largc ccllti
arranged like a fan so that the apices adjacent to the cndoHtylar
groove are closely crowded while the bases are widely spread adjacent
to the underlying blood spaces. The individual cells have a basal
nucleus, extensively folded endoplasmic reticulum, numerous secretory
vesicles and surface microvilli. The basal membrane of the cell is a h
deeply folded, especially in zone 2, indicating that considerable metabolic exchange must occur between these cells and the blood spaces.
The dr4iails of the fine structure are fully illuatrated by Aros and
Virtigh (1969), 1,evi and Porte ( 1!164) and Godeaux and Firket (1968)
23
IV. THE I':NDOSTYLE
The endostyle f'ormn a shdlow groove extending along the whole
length of the ventrnl side of the braiichial sac. The morphology and
histology of this structure hax been reviewed by a number of authors
including Soldska (1931), Raimbault ( I 948), Barrington (1957),
Olsson (1963) and Orsi and Relini (I966a,b) and details of ultrastructure and histoohemistry of the various regions are given by Levi
and Yorte (1964), Godeiiux am1 Firket, (1966, I968), Ghiani et al.
( 1 965), Ghiani and Orsi ( 1 !Isti), Aros and Vir&gh (1 MI)), Godeclux (1 97 I )
and Thorpc PI aE. (1972).
'I'herr is roirsiderablc uniformity in t h structure of the endostyle in
different specivs aiid in gcneriil it is dividod into eight regions or zones
as illustrated in Fig. H. An idditional small group of cells between
zones 4 iintl 5 has becn drsrribed by Orsi m d Relini (1966a) and
Codeaux and Firket ( 1 968) wid another small group between zones 7
and 8 in the family Pyuridar by Orsi and Relini (1986a,b) and in
Ciona by 'l'hirbold (197 I ) .
Zone 1 at the base of the groove is unpaired and is composed of tall
cells arraiigcd on either side of' a groove marking the median plane of
the endostyle. Thrse cells con1 ain large, electron dense granules about
700 A in diameter and a number of microtubules and microfibrils.
A t the apex the cells bear l o ~ g flagella surrounded at their base by
numerous finger-like microvilli (Godeaux and Firket, 1968 ; Ghiani and
Orsi, 1966 ; AroH and Virligh, I969). Arcording to many authors these
cells produce i i secretion of mumis (Levi and Porte, 1964 ; Barrington,
1957; Ghiani and Orsi, 1966: T h o r p ~t al., 1!172), but Olsson (1963)
itlid Godeaux and Firkct ( I96H) 110th considrr that the granular contents of the cell are glycwgen and not mucus. The flagella appear to be
used to sprestl secretions from other zones throughout the enclostylar
groovc itnd to assist in wafting them out towardx tho walls of thc
hi*~nc~hi;il sac.
Zones 2 and 4 are composed of a nmall number of very largc ccllti
arranged like a fan so that the apices adjacent to the cndoHtylar
groove are closely crowded while the bases are widely spread adjacent
to the underlying blood spaces. The individual cells have a basal
nucleus, extensively folded endoplasmic reticulum, numerous secretory
vesicles and surface microvilli. The basal membrane of the cell is a h
deeply folded, especially in zone 2, indicating that considerable metabolic exchange must occur between these cells and the blood spaces.
The dr4iails of the fine structure are fully illuatrated by Aros and
Virtigh (1969), 1,evi and Porte ( 1!164) and Godeaux and Firket (1968)