1. THE PITUITARY GLAND
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the more recent information. The anatomy of the gland at first sight appears almost as varied as the teleosts themselves, but closer examination
shows that this superficial variety can be reduced to a common anatomical and histological pattern. A species in which the histophysiology of
the pituitary has been particularly fully investigated is the European eel,
Anguilla anguilla, in a long series of fundamentally important studies by
Olivereau. The gland has also been investigated in the cyprinodont
Poecilia lutipinna and P. formosd by the senior author and his collaborators. A description of the gland in these two teleosts will serve as a basis
for a general account of the teleostean pituitary, and notable departures
from these basic types will then be considered.
1. THE EEL, AnguiZZa anguilla
Olivereau ( 1967a ) has recently summarized her extensive experimental investigations of the eel pituitary (Fig. 1). The two primary divisions
of the gland are obvious, with the central neurohypophysis interdigitating
with the shell-like adenohypophysis. The adenohypophysis may be further divided into two main parts: anteriorly the pars distalis, subdivided
into rostral and proximal pars distalis, on the basis of cell types; and
posteriorly a pars intermedia. As usual in teleosts, the interdigitations of
the neurohypophysis with the pars intermedia are particularly deep and
elaborate, while the neurohypophysial-pars distalis interdigitations are
less pronounced.
The terminology applied to the fish pituitary was for many years in
a state of confusion, and a new terminology introduced by Pickford and
Atz (1957) helped to introduce some uniformity. On this scheme the
rostral pars distalis was termed the “pro-adenohypophysis,” the proximal
pars distalis was termed the “meso-adenohypophysis,” and the pars intermedia was termed the “nieta-adenohypophysis.” At the time they were
introduced these terms were valuable in preventing the too easy assumption of the functions of the various regions implicit in applying the mammalian terms “pars distalis” and “pars intermedia” to the fish gland. However, advances in our knowledge of the functions of the various cells in
the teleost gland during the past 10 years or so have rendered this terminology in some respects misleading. Current evidence, reviewed below,
implies that the pro- and meso-adenohypophysis together form the functional equivalent of the tetrapod pars distalis, and the meta-adenohypophysis is equivalent to the pars intermedia; this being so, there is no
reason to accord each of these three regions in the teleost gland equal no* Throughout this review, any observations on Poecilia quoted without references
come from unpublished work by J. N. Ball and collaborators.
5
the more recent information. The anatomy of the gland at first sight appears almost as varied as the teleosts themselves, but closer examination
shows that this superficial variety can be reduced to a common anatomical and histological pattern. A species in which the histophysiology of
the pituitary has been particularly fully investigated is the European eel,
Anguilla anguilla, in a long series of fundamentally important studies by
Olivereau. The gland has also been investigated in the cyprinodont
Poecilia lutipinna and P. formosd by the senior author and his collaborators. A description of the gland in these two teleosts will serve as a basis
for a general account of the teleostean pituitary, and notable departures
from these basic types will then be considered.
1. THE EEL, AnguiZZa anguilla
Olivereau ( 1967a ) has recently summarized her extensive experimental investigations of the eel pituitary (Fig. 1). The two primary divisions
of the gland are obvious, with the central neurohypophysis interdigitating
with the shell-like adenohypophysis. The adenohypophysis may be further divided into two main parts: anteriorly the pars distalis, subdivided
into rostral and proximal pars distalis, on the basis of cell types; and
posteriorly a pars intermedia. As usual in teleosts, the interdigitations of
the neurohypophysis with the pars intermedia are particularly deep and
elaborate, while the neurohypophysial-pars distalis interdigitations are
less pronounced.
The terminology applied to the fish pituitary was for many years in
a state of confusion, and a new terminology introduced by Pickford and
Atz (1957) helped to introduce some uniformity. On this scheme the
rostral pars distalis was termed the “pro-adenohypophysis,” the proximal
pars distalis was termed the “meso-adenohypophysis,” and the pars intermedia was termed the “nieta-adenohypophysis.” At the time they were
introduced these terms were valuable in preventing the too easy assumption of the functions of the various regions implicit in applying the mammalian terms “pars distalis” and “pars intermedia” to the fish gland. However, advances in our knowledge of the functions of the various cells in
the teleost gland during the past 10 years or so have rendered this terminology in some respects misleading. Current evidence, reviewed below,
implies that the pro- and meso-adenohypophysis together form the functional equivalent of the tetrapod pars distalis, and the meta-adenohypophysis is equivalent to the pars intermedia; this being so, there is no
reason to accord each of these three regions in the teleost gland equal no* Throughout this review, any observations on Poecilia quoted without references
come from unpublished work by J. N. Ball and collaborators.