1. THE PITUJTARY GLAND
7
menclature status, nor is there any point in withholding from them the
names of their tetrapod equivalents. Thus, we prefer the terminology
adopted by the Division of Comparative Endocrinology of the American
Society of Zoologists ( Gorbman, 1965a) , and in general use for the teleost
pituitary by many workers on histophysiology (see Olivereau, 1963a,b;
Olivereau and Ball, 1964). A further reason for uniting pro-adenohypophysis and meso-adenohypophysis as a single pars distalis, as pointed
out by Olivereau ( 1962c, 1963a,b; Olivereau and Ball, 1964), is that certain cell types occur in different species in either the rostral or the proximal regions of the pars distalis, or even in both regions (Sections 11, By 4
and 11, B, 5); there can be no doubt that taken together the pro-adenohypophysis and meso-adenohypophyses have the same complement of
cell types and function as the pars distalis of tetrapods. Any division into
rostral pars distalis and proximal pars distalis is merely a matter of descriptive convenience, and no longer should be taken to indicate some
fundamental and constant distinction equivalent to the separation of pars
intermedia and pars distalis. The dangers inherent in accepting the fundamental nature of the rostral-proximal division of the pars distalis are
illustrated by the idea current a few years ago that the pro-adenohypophysis was in some way peculiar to fishes, with no homolog in the tetrapod
gland (Dodd, 1963), and even that the meso-adenohypophysis was the
homolog of the entire pars distalis of tetrapods (Dodd and Kerr, 1963),
although at that time the cells secreting prolactin and ACTH (and which
in fact both occur in the rostral pars distalis) had not been identified (cf.
discussion of Wingstrand, 1966a).
In the eel the rostral pars distalis includes three cell types. The 7 cells
( prolactin cells) are arranged in follicles, a feature typical of the more
primitive teleosts. Centrally, between these follicles, occur masses and
cords of 6 cells (TSH cells), while at the posterior border of the rostral
region with the neurohypophysis is a layer of cells ( ACTH cells) (Fig.
1). The proximal pars distalis in the eel includes two cell types arranged
in cell cords running more or less vertically. Most of the cells are (Y cells
(growth hormone cells), and they are mixed with gonadotrops, of which
there are two types. The pars intermedia includes two cell types, the precise functions of which are uncertain. The neurohypophysial fibers contain typical masses and grains of neurosecretory material; even when, as
Herring bodies, these accumulations are very large, they are in fact contained within the swollen nerve fibers (Lederis, 1964). This stainable
neurosecretory material is usually particularly abundant in the posterior
part of the neurohypophysis, where it interdigitates with the pars intermedia. The neurohypophysis also contains scattered cells ( pituicytes ) of
uncertain function ( Section 11, C ).
7
menclature status, nor is there any point in withholding from them the
names of their tetrapod equivalents. Thus, we prefer the terminology
adopted by the Division of Comparative Endocrinology of the American
Society of Zoologists ( Gorbman, 1965a) , and in general use for the teleost
pituitary by many workers on histophysiology (see Olivereau, 1963a,b;
Olivereau and Ball, 1964). A further reason for uniting pro-adenohypophysis and meso-adenohypophysis as a single pars distalis, as pointed
out by Olivereau ( 1962c, 1963a,b; Olivereau and Ball, 1964), is that certain cell types occur in different species in either the rostral or the proximal regions of the pars distalis, or even in both regions (Sections 11, By 4
and 11, B, 5); there can be no doubt that taken together the pro-adenohypophysis and meso-adenohypophyses have the same complement of
cell types and function as the pars distalis of tetrapods. Any division into
rostral pars distalis and proximal pars distalis is merely a matter of descriptive convenience, and no longer should be taken to indicate some
fundamental and constant distinction equivalent to the separation of pars
intermedia and pars distalis. The dangers inherent in accepting the fundamental nature of the rostral-proximal division of the pars distalis are
illustrated by the idea current a few years ago that the pro-adenohypophysis was in some way peculiar to fishes, with no homolog in the tetrapod
gland (Dodd, 1963), and even that the meso-adenohypophysis was the
homolog of the entire pars distalis of tetrapods (Dodd and Kerr, 1963),
although at that time the cells secreting prolactin and ACTH (and which
in fact both occur in the rostral pars distalis) had not been identified (cf.
discussion of Wingstrand, 1966a).
In the eel the rostral pars distalis includes three cell types. The 7 cells
( prolactin cells) are arranged in follicles, a feature typical of the more
primitive teleosts. Centrally, between these follicles, occur masses and
cords of 6 cells (TSH cells), while at the posterior border of the rostral
region with the neurohypophysis is a layer of cells ( ACTH cells) (Fig.
1). The proximal pars distalis in the eel includes two cell types arranged
in cell cords running more or less vertically. Most of the cells are (Y cells
(growth hormone cells), and they are mixed with gonadotrops, of which
there are two types. The pars intermedia includes two cell types, the precise functions of which are uncertain. The neurohypophysial fibers contain typical masses and grains of neurosecretory material; even when, as
Herring bodies, these accumulations are very large, they are in fact contained within the swollen nerve fibers (Lederis, 1964). This stainable
neurosecretory material is usually particularly abundant in the posterior
part of the neurohypophysis, where it interdigitates with the pars intermedia. The neurohypophysis also contains scattered cells ( pituicytes ) of
uncertain function ( Section 11, C ).