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A. M. PERKS
neutral principle which never amounted to more than 3.9% of the total
oxytocic activity of the major hormonal constituent, which was probably
arginine vasotocin. It can be concluded that the chondrosteans so far
examined appear to contain mainly arginine vasotocin, with small,
perhaps variable, amounts of an unidentified neutral principle. This is
the reverse situation to that seen in the elasmobranchs.
C. The Actions of Neurohypophysial Principles in the Chondrostei
There are no direct experiments on the effects of neurohypophysial
principles in the Chondrostei. Again the presence of a median eminence,
and the close association of the pars nervosa with the pars intermedia,
suggest that the neurohypophysis could be important in the local control
of the adenohypophysis. However, anatomical considerations indicate
that neurohypophysial principles could also escape into the general
circulation. The only suggestion of their possible influence outside the
pituitary comes from the histological studies of Barannikova and Polenov
(1960). These workers noted that there were seasonal changes in the
distribution of neurosecretion within the neurohypophysis. Fish in the
Volga showed neurosecretion localized mainly in the preoptic nucleus in
the spring and mostly in the pars nervosa during autumn. Specimens
taken in the North Caspian Sea, at the point of migration and spawning,
possessed a preoptic nucleus rich in vacuoles and neurosecretion. Such
observations are difficult to interpret. Barannikova and Polenov (1960)
suggested that the neurohypophysis was concerned in “certain vegetative
functions,” and they appeared to be impressed by changes in the activity
of the thyroid. However, comparison with other observations in the
teleosts suggests that the principles in the Chondrostei might be important
in spawning or egg laying (see Section VIII ) .
VII. BONY FISH: THE HOLOSTEI
A. The Structure of the Neurohypophysis of the Holostei
It is probable that the Holostei, the bowfins and the garpike, are more
closely related to the teleost fish than are the other “preteleost” groupsthe brachiopterygians and the Chondrostei. Therefore, it is not surprising
that their general pituitary structure has been said to be similar to that of
the teleost bony fish (e.g., Wingstrand, 1966). However, this is only
partly true of the neurohypophysis, for the recent work of Sathyanesan
A. M. PERKS
neutral principle which never amounted to more than 3.9% of the total
oxytocic activity of the major hormonal constituent, which was probably
arginine vasotocin. It can be concluded that the chondrosteans so far
examined appear to contain mainly arginine vasotocin, with small,
perhaps variable, amounts of an unidentified neutral principle. This is
the reverse situation to that seen in the elasmobranchs.
C. The Actions of Neurohypophysial Principles in the Chondrostei
There are no direct experiments on the effects of neurohypophysial
principles in the Chondrostei. Again the presence of a median eminence,
and the close association of the pars nervosa with the pars intermedia,
suggest that the neurohypophysis could be important in the local control
of the adenohypophysis. However, anatomical considerations indicate
that neurohypophysial principles could also escape into the general
circulation. The only suggestion of their possible influence outside the
pituitary comes from the histological studies of Barannikova and Polenov
(1960). These workers noted that there were seasonal changes in the
distribution of neurosecretion within the neurohypophysis. Fish in the
Volga showed neurosecretion localized mainly in the preoptic nucleus in
the spring and mostly in the pars nervosa during autumn. Specimens
taken in the North Caspian Sea, at the point of migration and spawning,
possessed a preoptic nucleus rich in vacuoles and neurosecretion. Such
observations are difficult to interpret. Barannikova and Polenov (1960)
suggested that the neurohypophysis was concerned in “certain vegetative
functions,” and they appeared to be impressed by changes in the activity
of the thyroid. However, comparison with other observations in the
teleosts suggests that the principles in the Chondrostei might be important
in spawning or egg laying (see Section VIII ) .
VII. BONY FISH: THE HOLOSTEI
A. The Structure of the Neurohypophysis of the Holostei
It is probable that the Holostei, the bowfins and the garpike, are more
closely related to the teleost fish than are the other “preteleost” groupsthe brachiopterygians and the Chondrostei. Therefore, it is not surprising
that their general pituitary structure has been said to be similar to that of
the teleost bony fish (e.g., Wingstrand, 1966). However, this is only
partly true of the neurohypophysis, for the recent work of Sathyanesan