TlIE PIiYSIOI.OQY OF AYCIDIANS
113
There is thus a very close link brtween nerve ganglion and neural
gland in development and they remain in close association to one
another in adult life. The origins and close association of these two
structures has lcd many workers to consider the neural gland as the
homologue of the vertebrate pituitary, but if this is so it can only
represent the pars nervosa and not the whole pituitary. Furthermore
the vertebrate pituitary is an entirely endocrine structure while the
neural gland appcam to be primarily exocrine.
C . Functione of the neural gland
In spite of extensive research by a number of workers we appear
still to be very far from understanding the true functions of the neural
gland. Reviews on this subject have already been written by Butcher
(1930), Huus (1937), Carlisle (1951) and Dodd and Dodd (1966). We
have seen in the previous section that on purely embryological grounds
it cannot be homologized with the whole pituitary, but only with the
posterior lobe. Furthermore the histological evidence presented above
suggests Lt n exocrine rather than an endocrine function. Nevertheless
numerous attempts have been made to establish the presence of pituitary-like hormones in the neural gland or neural complex (i.e. neural
gland plus gangliori). These studies may be divided into those seeking
posterior pituitary hormones, nuch as oxytocin, vasopressin and
melanocyte stimulating hormone, and those which seek the presence of
adenohypophysial hormones such as gonadotrophin ; they are treated
separately below.
1. Oxytocin and vmopresein
Butcher (1 930), on the basis of tt sitigle extract of fifty gland8 from
Giona inteetinazis, claimed that oxytocin was present in the complex at a
strength comparable to mammalian pituitary extracts. Bacq and Florkin (1935, 1946) also reported the presence of oxytocin as bell as a
vasopressin and a melanocyte stimulating hormone (MSH), but PBrh
(1943, 1947a,b) found that oxytocic activity, while admittedly present,
was not confined to the neural complex but was found in many other
tissues; he conclitded that it was probably a histamine and not an
oxytocin. Sawyer (1959) also demonstrated the presence of oxytocic
activity in both neural complex and in other tiesues, but he found sufficient differences in its physiological behaviour to lead him to conclude
that it was not ltctually oxytocin, but a substance which mimics
oxytocin. Sawycr was unable to detect any vasopressor activity in
neural complex extracts, and found a very weak anti-diuretic activity
in Pyura only, which he considered to be non-specific.
113
There is thus a very close link brtween nerve ganglion and neural
gland in development and they remain in close association to one
another in adult life. The origins and close association of these two
structures has lcd many workers to consider the neural gland as the
homologue of the vertebrate pituitary, but if this is so it can only
represent the pars nervosa and not the whole pituitary. Furthermore
the vertebrate pituitary is an entirely endocrine structure while the
neural gland appcam to be primarily exocrine.
C . Functione of the neural gland
In spite of extensive research by a number of workers we appear
still to be very far from understanding the true functions of the neural
gland. Reviews on this subject have already been written by Butcher
(1930), Huus (1937), Carlisle (1951) and Dodd and Dodd (1966). We
have seen in the previous section that on purely embryological grounds
it cannot be homologized with the whole pituitary, but only with the
posterior lobe. Furthermore the histological evidence presented above
suggests Lt n exocrine rather than an endocrine function. Nevertheless
numerous attempts have been made to establish the presence of pituitary-like hormones in the neural gland or neural complex (i.e. neural
gland plus gangliori). These studies may be divided into those seeking
posterior pituitary hormones, nuch as oxytocin, vasopressin and
melanocyte stimulating hormone, and those which seek the presence of
adenohypophysial hormones such as gonadotrophin ; they are treated
separately below.
1. Oxytocin and vmopresein
Butcher (1 930), on the basis of tt sitigle extract of fifty gland8 from
Giona inteetinazis, claimed that oxytocin was present in the complex at a
strength comparable to mammalian pituitary extracts. Bacq and Florkin (1935, 1946) also reported the presence of oxytocin as bell as a
vasopressin and a melanocyte stimulating hormone (MSH), but PBrh
(1943, 1947a,b) found that oxytocic activity, while admittedly present,
was not confined to the neural complex but was found in many other
tissues; he conclitded that it was probably a histamine and not an
oxytocin. Sawyer (1959) also demonstrated the presence of oxytocic
activity in both neural complex and in other tiesues, but he found sufficient differences in its physiological behaviour to lead him to conclude
that it was not ltctually oxytocin, but a substance which mimics
oxytocin. Sawycr was unable to detect any vasopressor activity in
neural complex extracts, and found a very weak anti-diuretic activity
in Pyura only, which he considered to be non-specific.