2. THE NEUROHYPOPHYSIS
181
1966). During the embryology of Protopterus aethiopicus, the neural tissue
is invaded by solid strands of ependymal cells, which extend from the ventricle, and then open up to form a tubular lumen along much of their length
(Kerr and Van Oordt, 1966). Dodd and Kerr (1963) have remarked that
the pars nervosa of Protopterus annectens does not contain a great proportion of neural tissue, since so much of its structure is composed of ependyma1 cells, spaces, lumina of tubules, and blood vessels. Nevertheless,
the pars nervosa is penetrated by the axons of the preoptico-hypophysial
tract, and the fibrous matrix is heavily laden with neurosecretory material
( Protopterus annectens: Dorn, 1957; Dodd and Kerr, 1963; Wingstrand,
1966; P. aethiopicus, Kerr and van Oordt, 1966). Some axons spread into
the ependyma of the dorsal wall of the infundibular cavity, where Herring
bodies have been seen close to the cerebrospinal fluid (Protopterns
annectens; Dorn, 1957). Kerr and van Oordt (1966) have noted the
presence of occasional pituicytes in the pars nexvosa of Protopterus
aethw picus.
The outer surfaces of the neural processes and tubules are often
associated with the tissue of the pars intermedia. The intermedia tissue lies ventral to them, and it is largely separated from the rest of the
adenohypophysis by a hypophysial cleft-except in the case of adult
specimens of Protopterus aethiopicus, where this cleft is partly occluded
( Lepidosiren sp., Charipper, 1937; Protopterus annectem, Wingstrand,
1959a; Dodd and Kerr, 1963; P . aethiopicus, Kerr and van Oordt, 1968). In
species of Protoptew, the pars intermedia is mainly composed of tubules,
like the pars nervosa; the cords of intermedia cells are divided by hollow
spaces and by tubelike extensions from the hypophysial cleft ( Protopterus
annectem, Dodd and Kerr, 1963; Wingstrand, 1966; P . aethiopim, Kerr
and van Oordt, 1966). The extent to which the pars nervosa penetrates
and intermingles with the pars intermedia appears to vary between
different species. A comparison of different authors suggests that intermingling is least marked in species of Lepidosiren, where the pars intermedia is particularly thin (Charipper, 1937; Kerr, 1949; Wingstrand,
1966). In Neoceratodus forsteri the invasion of neural elements into the
pars intermedia appears to be more marked ( Griffiths, 1938; Kerr, 1949).
In Protopterus annectens and P . dolloi, the intimate intermingling of the
two tissues recalls that typical of fish, and not the more discrete and
self-contained pattern of the tetrapods (Dodd and Kerr, 1963; Kerr and
van Oordt, 1966). In adult specimens of Protopterus aethiopicus there
is a highly complicated interdigitation between columns and tubules extending from both the pars nervosa and the pars intermedia (Dawson,
1940; Kerr, 1949; Kerr and van Oordt, 1966).
Despite this intimate intermixing of neural and intermediate tissues,
181
1966). During the embryology of Protopterus aethiopicus, the neural tissue
is invaded by solid strands of ependymal cells, which extend from the ventricle, and then open up to form a tubular lumen along much of their length
(Kerr and Van Oordt, 1966). Dodd and Kerr (1963) have remarked that
the pars nervosa of Protopterus annectens does not contain a great proportion of neural tissue, since so much of its structure is composed of ependyma1 cells, spaces, lumina of tubules, and blood vessels. Nevertheless,
the pars nervosa is penetrated by the axons of the preoptico-hypophysial
tract, and the fibrous matrix is heavily laden with neurosecretory material
( Protopterus annectens: Dorn, 1957; Dodd and Kerr, 1963; Wingstrand,
1966; P. aethiopicus, Kerr and van Oordt, 1966). Some axons spread into
the ependyma of the dorsal wall of the infundibular cavity, where Herring
bodies have been seen close to the cerebrospinal fluid (Protopterns
annectens; Dorn, 1957). Kerr and van Oordt (1966) have noted the
presence of occasional pituicytes in the pars nexvosa of Protopterus
aethw picus.
The outer surfaces of the neural processes and tubules are often
associated with the tissue of the pars intermedia. The intermedia tissue lies ventral to them, and it is largely separated from the rest of the
adenohypophysis by a hypophysial cleft-except in the case of adult
specimens of Protopterus aethiopicus, where this cleft is partly occluded
( Lepidosiren sp., Charipper, 1937; Protopterus annectem, Wingstrand,
1959a; Dodd and Kerr, 1963; P . aethiopicus, Kerr and van Oordt, 1968). In
species of Protoptew, the pars intermedia is mainly composed of tubules,
like the pars nervosa; the cords of intermedia cells are divided by hollow
spaces and by tubelike extensions from the hypophysial cleft ( Protopterus
annectem, Dodd and Kerr, 1963; Wingstrand, 1966; P . aethiopim, Kerr
and van Oordt, 1966). The extent to which the pars nervosa penetrates
and intermingles with the pars intermedia appears to vary between
different species. A comparison of different authors suggests that intermingling is least marked in species of Lepidosiren, where the pars intermedia is particularly thin (Charipper, 1937; Kerr, 1949; Wingstrand,
1966). In Neoceratodus forsteri the invasion of neural elements into the
pars intermedia appears to be more marked ( Griffiths, 1938; Kerr, 1949).
In Protopterus annectens and P . dolloi, the intimate intermingling of the
two tissues recalls that typical of fish, and not the more discrete and
self-contained pattern of the tetrapods (Dodd and Kerr, 1963; Kerr and
van Oordt, 1966). In adult specimens of Protopterus aethiopicus there
is a highly complicated interdigitation between columns and tubules extending from both the pars nervosa and the pars intermedia (Dawson,
1940; Kerr, 1949; Kerr and van Oordt, 1966).
Despite this intimate intermixing of neural and intermediate tissues,